RN Subs

9. The programmes and total cost per boat were:

The 1906-07 Programme was originally for ten boats by contract and two boats at Chatham. This number was eventually cut to eight to satisfy a general policy of economy and the programme revised by ordering seven C Class and D1.

Vickers built all the boats mentioned above except two boats in each of the Programmes of 1906-07, 1907-08 and 1908-09 were placed with Chatham Dockyard, C17-20 and C33-34. This table of costs was prepared in 1912 and it may be assumed are actual costs on fixed price contracts. The costs of the boats built at Chatham undoubtedly varied from these figures.

10. Lipscombe states 'the Holland Class never lost a man from any cause', which was exceptional in such small, novel and rather precarious boats. Holland Nos 1-3 were sold in October 1913 to T W Ward, the shipbreakers, for £410, £360 & £405 respectively and Holland No 5 was lost whilst in tow from Portsmouth to Sheerness in August 1912. Holland No 4 was sunk by shellfire during experiments in October 1912.

3.3 Design

11. The contract for the Holland boats between Messrs Vickers, Sons & Maxim Ltd and the Admiralty was to supply repeats in all particulars of the Holland boats then building for the US Navy. It included certain guaranteed conditions of performance as shown in Paragraph 6. The Admiralty letter of 13 December 1900, mentioned in Paragraph 3 above, states submarine boats of the Holland Type No. 7, This was an error.

A little background to the American design is therefore appropriate. In 1895 a contract was signed by the United States Government with the Holland Torpedo Boat Company for a submarine designed by Mr J P Holland (his Holland No 7) which was subsequently named the Plunger. It is stated by Lake to have been 85 feet long x 11½ feet in diameter, 153 tons surface displacement and 186 tons submerged. After launching in August 1897 it was never completed at the Company's request. They built another boat Holland No8, which was not entirely satisfactory and then Holland, No 9. The characteristics of the latter are given by Fyfe as length 53 feet 10 inches, diameter 10 feet 3 inches, displacement 75 tons, main ballast water 10 tons, reserve of buoyancy 250lbs (meaning here in the 'awash' condition). It was fitted with a 50 HP Otto gasoline engine to give a surface speed of 7 knots. A motor of 150 HP for two hours and 50 HP for six hours with a battery of 66 cells giving 350 amps for four hours and submerged speed 8 knots (Lake gives 5 knots). Surface endurance 150 miles at 7 knots and submerged endurance 50 miles maximum. It had two tubes, one forward and one aft to fire aerial torpedoes or shells (the after one was later deleted) and one tube forward to discharge 18in Whitehead torpedoes. This submarine joined the US Navy on 11 April 1900.

A contract was then made by the US Government with the Holland Boat Company for a further six boats, Nos 3-8, the Adder Class to an improved design. Fyfe it states that the USN Nos 3-8 resembled in almost every particular those for the Holland Nos 1-5 built by the RN. Sueter states that the specification for the British boats was that for Holland No 10 obviously USN Nos 3-8. There has been some controversy over the Holland type used for the RN boats, but it was obviously No 10.

12. The Westminster Gazette of 20 August 1901 published a statement to the effect that five submarines were being built for the RN and gave the following account:

The speed laid down is 8 knots in fine weather and 7 knots in ordinary weather. They are 63 feet 4 inches long, 11 feet 9 Inches beam and 120 tons displacement; 160 HP with an endurance of 400 miles and a surface speed of 9 knots. The battery is capable of 4 hours at 7 knots. They carry 5 torpedoes each 11 feet 8 inches long.

This was before Holland No 1 was launched and was probably the first account of a British submarine published in the press. The limited knowledge in the Admiralty of the design may be judged by the fact that in DNC's records the dimensions quoted in the press report were confirmed by deduction from a drawing. As far as can be ascertained and in fact as would have been expected no detailed specifications or working drawings were submitted to the Admiralty for approval although overseers were appointed to see that 'proper materials were put into the boats'. Captain Bacon RN DSO was appointed to Barrow as inspecting Captain of Submarines.

13. The Holland Boat Company supplied a set of working plans to Vickers. This must have been late 1900 or early 1901 since Holland No 1 was laid down on the 4 February 1901. Some notes prepared at Vickers in 1925 on the events that followed read on the following lines:

Investigation of these first plans resulted in a considerable number being scrapped as useless and drastic alterations were made during the progress of the work so as to produce a workable submarine. For example, about 56% only of the design main ballast was possible and too much trimming ballast was required. Steering and diving gears were impracticable and were entirely redesigned by us and the same applied to various details of these boats. After experience of the first boat the Admiralty, through Captain Bacon, objected to the presence of the Electric Boat Company's (Holland Boat Co) guarantee engineer and he was removed.

From then on the serious work of designing and developing the British submarine by Vickers commenced and technical communications or advice from Electric Boat Company ceased under the official secrets regulations, nor was the Electric Boat Company technical advice, plans or assistance necessary from that time onwards.

The A1, the first boat to be designed by Vickers followed, was 3 knots faster than the Holland's and in every way a success.

The A Class, B Class and C Class followed of entirely Vickers design and differed in every respect from any other known type of submarine. No American details or patents were used in any way. After, upwards of sixty submarines had been constructed and put into service the Admiralty commenced, officially, to supply their own outline design in the tender enquiries. Their first boat in this respect was D1, but Vickers at the same time were required to make such modifications as were necessary, whereby the firm undertook full responsibility regarding the ultimate performance, stability etc of the boat. All boats were accepted on sea trials.

This of course was written nearly twenty-five years after the event but it seems that from the start Vickers suffered considerable frustration. This was probably due to the problem of distance and communication between Barrow and America. Furthermore, as many authorities state, the RN Holland's were to be identical with the USN Adder Class, which were ordered 25 August 1900. The first of class Adder was launched in July 1901 and went on trials in November 1902. The first diving trials of Holland No 1 took place in February 1902 and deep-sea trials in April 1902. Holland No 2 and No 3 were completed some months before Adder. The point is that Vickers were building ahead of the Adder and its final working drawings before snags, and there must have been many of them, had been Ironed out In America. There must have been frustration on both sides with Vickers getting ahead of the prototype vessel. What Vickers say about the main ballast and the steering and hydroplanes was very true and the Americans must have found the same troubles before Adder, which was a very successful boat, was completed.

A critical factor in these boats was weight and an extra two or three tons added during building could account for the statement that 156% only of the design main ballast was possible'. In the RN Holland's, No 2 main ballast tank could not be used. It is not known whether this happened in the Adder Class but no mention that it did has been seen. As an example, by the American specification the plating was 8/20 in (16lb) thick amidships. The plating in the British Holland's was 17½lb equivalent to an addition in weight of about 40lb per foot run amidships. 'Many improvements were made during building' and 'many items redesigned' all of which undoubtedly meant extra weight, even though of only a small amount individually.

14. Without doubt, Vickers did an outstanding job in the Holland boats in an extremely short time, only 14 months in Holland No 1 before going on trials. Without belittling this effort, it is perhaps unfortunate that Burgoyne in 1903 should record 'There is one fault in the British Holland's however, the interiors are fitted with pieces of mechanism, which might easily be dispensed with. What struck me, especially on board the American boats, (the author had an opportunity of inspecting several at Long Island in October 1902) was the wonderful amount of space - or elbow room - they possessed, which must make a great difference to the comfort of those managing the boats during trials'. Whatever truth there may be in this statement or in spite of it, Vickers had produced the Holland Class and severed connection with the Holland Boat Company. It is assumed the original contract was cancelled and another contract made between the Admiralty and Vickers. The statement in Paragraph 13 mentions that in their designs from A1 onwards they did not use any American patents. That being so it is difficult to find any items in the RN Hollands which Holland patents could have covered.

15. The success of the Holland boats resulted in a steady programme of submarine construction. A1 was a development of the Holland design prepared by Vickers acting on instructions from the Admiralty and the A Class, B Class and C Class followed. Starting with the D Class, a sketch design was prepared by the Admiralty. Vickers were still responsible for the detailed calculations of weight and stability etc and of course the detailed working drawings.

16. Even before the first Holland boat went on trials it was appreciated that they were limited in surface speed and endurance so A1 was made larger in an endeavour to eliminate these limiting factors, although it was known that foreign powers had experienced considerable difficulties with their larger boats. For a country with no service experience of submarines, whatsoever this was a bold step and a great change from the attitude held two years previously.

The same spindle hull form as in the Holland boats was used in A1 with the length increased by about 40 feet and the displacement by about two-thirds. By increasing the power of the main engine and main motor, the amount of gasoline carried and the size of the battery it was hoped to improve the speed and endurance in both the surface and submerged conditions. This was achieved in the surface condition and improved in later vessels of the class as further changes in power were made. Little gain in submerged performance over the Holland boats however resulted. One bad feature of the Holland boats - the low reserve of buoyancy on the surface - was no better in the A Class. In the following B Class and C Class it was improved by about 2% when first built but this increase slowly deteriorated in service.

After A1 had been well advanced it was decided that a larger torpedo armament was necessary. A2 onwards were redesigned with two bow tubes placed side by side as against one in A1. The form was changed in an effort to improve speed. The beam was increased and the lines made finer in the forward body and at the after end, but the fact that the lines right forward in way of the two tubes had to be made that much fuller largely nullified the improvement desired.

A1's first dive in the dock at Barrow was a great success and showed a big advance on the Holland's. At sea 'she behaved well and could keep an even depth at quite moderate speed whereas the earlier boats had to be trimmed fine and kept at full speed when working submerged'.

The dangers consistent with using gasoline and the advantages of adopting heavy oil engines were very obvious at this time and A13 was chosen to be fitted with one so, that exhaustive trials could be done. In consequence she did not complete until mid 1908.

Due to developments as this class was building, quite large variations occurred between individual boats. They are therefore treated as four types: A1, A2-4, A5-12, and A13.

17. The A Class were still limited in speed and endurance, the accommodation was cramped and they were liable to plunge in a swell. To improve these shortcomings, the B Class were increased in length by nearly 40 feet and in beam by 10 inches over the A Class and by 100 tons in surface displacement. They had the same spindle hull form and the same armament. The Wolseley type petrol engine of the A Class, but now made by Vickers was retained since no experience had yet been obtained with the heavy oil engine in A13. The Increase in surface speed was disappointing being only of the order of 0.5 knot, but there was a good increase in surface endurance. An increase of 0.5 knot submerged was achieved by increasing the motor power by over 40%. C1-18 were similar to the B Class except that by a further increase in power the submerged speed rose by another 0.5 knot. Modifications were made in C19-38 which greatly improved both surface and submerged speed.

Many improvements were made from B1 to C38 over the four years those two classes were building, in particular in the superstructure to improve surface running and seaworthiness. It is doubtful whether the standards of accommodation improved to any noticeable extent.

18. One, perhaps controversial feature of all these single hull boats and also in the D Class, is that they had no internal watertight bulkheads. A statement in Reference (5) by the DNC at the time is of interest. He states, 'The small size of the earlier boats and the undesirability of isolating from their officers the men controlling the operations vital in an emergency of flooding and emptying main ballast tanks, had prevented the subdivision of the main working space by watertight bulkheads. Although for other reasons this course is obviously -desirable'. At this time-centralised control of such operations in the control room had not been developed.

19. Drawings of these classes are shown in the following plates:

• Plate 1 - HOLLAND Class General Arrangement
• Plate 2 - A1 General Arrangement
• Plate 3 - A2-4 General Arrangement
• Plate 4 - A13 General Arrangement
• Plate 5 - B Class General Arrangement
• Plate 6 - B Class Construction Sections
• Plate 7 - Cl-11 General Arrangement
• Plate 8 - C21-30 General Arrangement

It can be assumed that A5-12 were built in accordance with Plate 3: except for minor differences given later. Similarly C12-18 were built in accordance with Plate 7: and C19-20 and C31-38 with Plate 8: DNC records sub-divide the C Class into C1-18 and C19-38.

Details of the main machinery and other equipment In these classes are given in Chapters 20-32.

20. A comparison of the relative merits of the designs in 1910 is given by Domville Fife who sums them up as follows:

Holland 1-5 were only moderately successful and had great trouble with petrol engines. They were erratic when submerged and the surface qualities were bad. However they had excellent diving qualities and could submerge in three minutes from full buoyancy when travelling. A1-4 were improved Holland's and were fitted with a high conning tower and short periscope. They showed only a slight improvement on the Holland's. A5-13, was an improvement on A1-4, B1-11 proved far superior to all preceding boats and are equal now to any foreign submarines afloat. C Class. Sea going submarines of great fighting value

Although one may not agree with this statement in some respects it does give a probably unbiased view of the advance made in submarine design over a very short period of only four years.

3.4 Form and Dimensions

21. Varying figures for the principal dimensions of the four classes have been quoted by various sources and because of secrecy at the time differences are to be expected. Only figures by Vickers and DNC have been considered. As far as possible differences are explained. The dimensions given in Appendix IIA are those considered to be the most reasonable to reflect the design and as the vessels should have been built.

22. The Holland boats were single hulled vessels of spindle form i.e. all transverse sections were completely circular with the centres of all sections on a straight line. The lines of the fore body were fuller than in the after body to give space in the fore end for an 18-inch bow torpedo tube. Because of the inherent unstable condition of this form when underway, vertical and horizontal fins were fitted at the after end. Plate bilge keels were also fitted to prevent the excessive rolling to be expected with a circular hull. It is however stated that these boats had a long period of roll and had almost an entire lack of rolling, but in a seaway had a peculiar flanking motion, which seemed to shift the boat bodily to one side. No records have been seen to confirm this, but with such low freeboard and reserve of buoyancy this is likely to be true. A typical spindle hull form is shown in Fig 3.1 of the Docking Plan for A5-12.

This spindle hull form was not a shape which lent itself to surface speed and was inclined to be dangerous through small longitudinal stability and low reserve of buoyancy. It was liable to plunge in a swell. Efforts were made in the following classes to remedy these defects at least in part and increase in size alone was some advantage.

The spindle hull form was retained in the A Class, B Class and C Class. In A2-13 an effort was made to better the form to improve speed. The maximum beam near amidships was increased and the lines in the forward body and at the extreme after end made finer. These efforts were however largely nullified since the introduction of a second bow tube made it necessary to make the sections right forward much fuller and the bows blunter than in A1. The submerged buoyancy however remained practically the same as in A1.

3.4.1 Length

23. Vickers records Loa 63ft 10in and Lbp 63ft 4 in for the Holland boats. The latter appears to be the length from the FP to the after edge of the rudder. Based on a Loa of 63ft 10in and by measurement from Plate 1: the Lbp was approximately 61ft 9 in and the Lph 58ft 6in

After completion DNC quoted Loa 64ft 0in and Lbp 58ft 6in. For the latter figure he was quoting the Lph which was a fairly common practice in the early boats. Later on DNC gave Loa 64ft 1in, Lbp 61ft 11¼ in. (and stated this to be the length between the perpendicular through the stem and the centre line of rudder) and Lph 58ft 7in. These latter figures would be as built and would vary between boats.

In A1 the Loa was increased by nearly 40ft over the Holland boats. Vickers quotes Loa 103ft 3in and a docking plan gave 102ft 10in. The design figure of 103ft 3in is taken. Based on this the Lbp was 100ft 9 in and the Lph 93ft 6 in. A small space 2ft long at the extreme after end is not included in the pressure hull since access was impossible and it was probably open to the sea.

In A2-13 the Loa was increased over A1 by 1ft 9½in to accommodate the extra bow tube. Vickers quote a design Loa of 105ft 0½in but their figure for Lbp of 100ft is a misinterpretation and was actually 102ft 6in. The Lph was 96ft 0 in, but this measurement depends on the point chosen as the forward end of a complicated casting.

The length of the B Class and C Class was increased over the A Class by nearly 40ft. The designed Loa of 142ft 2½in is confirmed by as-built figures taken at Chatham Dockyard for C17 of 142ft 2½in and for C18 of 142ft 2in. Chatham Dockyard gave as built figures for the length of the pressure hull, stating that this is from the 'after end of the stern casting to after end of bow casting', as 132ft 2¼ in for C17 and 132ft 2-5/16in C18 as against a design figure of 132ft 2-3/8in. The bow casting mentioned is a cast bulkhead 2ft 6in from the FP. The designed Lbp has been quoted as 135ft. This figure is actually the distance between the stem (FP) and the after end of the pressure hull. The Lbp was about 139 ft 4 in.

3.4.2 Beam

24. Without doubt the moulded diameter of the pressure hull in the Holland boats was 11ft 9 in, but there are various statements about the thickness of plating and how it was worked. Sueter gives ten strakes of 8/20in plating amidships. Domville-Fife states seven strakes of 7/20in plating. From the plating thicknesses given these two references were quoting from American sources. Vickers record 7/16in plating.

DNC records state 'the bottom plating was 7/16in thick and the plates to frames were ½in thick. He also gave the extreme beam as 11ft 10in. This suggests that the pressure hull plating was worked in raised and sunken strakes which it certainly was in the A Class, B Class and C Class, and that the plates at the maximum beam were inner strakes of ½in. plating. In curves of stability prepared by DNC in 1905 the maximum diameter of the hull used in the calculations was 11.86ft. This figure agrees with the statement but from Vickers' records it applies to A1.

From the evidence available it is assumed that in the Holland boats the plating was worked as in the later classes, that is in eight strakes of plating with raised and sunken strakes, with sunken strakes at the maximum beam and the keel as shown in Plate 6. The top plate of the pressure hull was without doubt a raised strake. This does not agree with detailed figures given by Vickers, which give the same maximum beam and depth in all classes. It can only be assumed that this top raised strake was flattened in the middle to touch the frame line.

25. The design maximum moulded diameter of the pressure hull in the Holland Class was 11ft 9 in. Figures for maximum beam have been seen varying between 11ft 9 in and 11ft 11in. This is undoubtedly due to misinterpretation because any of four figures could have been quoted and not fully defined:

• If t = thickness of hull plating and
• D = moulded diameter of pressure hull
• D + 2t = maximum beam (inner strakes)
• D + 4t = maximum diameter to outside of plating (outer strakes)
• D + 3t = diameter used in calculating buoyancy to outside of shell plating

The following seem to be correct for the Holland Class - moulded beam 11ft 9 in, maximum beam 11ft 9-7/8in, maximum diameter to outside of hull plating 11ft 10¾in.

The maximum moulded diameter in A1 remained the same as in the Holland boats at 11ft 9 in. It is stated that the pressure hull plating was increased to ½in (20lb) although Vickers records still show 7/16in (171lb) plating for all the A Class. At the same time they give the maximum depth as 11ft 10in and a docking plan of A1 gives the maximum diameter to outside of plating as 11ft 10-7/8in. This suggests that the inner strakes were 20lb plating and the outer strakes 17½lb plating and in accordance with DNC's statement mentioned in Paragraph 24. For the purpose of arriving at a figure it is taken that this did in fact happen. On the assumption that inner strakes of ½in plating were fitted at the maximum beam the figures became moulded diameter 11ft 9 in, maximum beam 11ft 10in, maximum diameter to outside of plating 11ft 10-7/8in.

In A2-13 the moulded beam was increased to 12ft 7¾in. Using the same thickness of plating as in A1 the maximum beam was 12ft 8¾in and the maximum diameter to outside of plating 12ft 9-5/8in. This latter figure is the one given on the docking plan as the diameter at Frame 30.

The moulded beam of the B Class and C Class was increased to 13ft 6in and all the plating amidships was 20lb, which gave a maximum beam of 13ft 7in as designed. This is confirmed by measurements taken at Chatham Dockyard of C17, C18 and C19 which were 13ft 7-3/16in, 13ft 7-3/16in and 13ft 7¼ in maximum beam as built, with the measured moulded beam being 1in less in each case. These figures show that the boats were built slightly larger than designed which would increase buoyancy by perhaps one ton and the right way.

3.4.3 Depth

26. Because all these classes were of circular section the moulded and maximum depths are the same as the moulded and aximum beams, except that the later boats in the C Class were fitted with a docking keel which increased the overall depth by 5½in.

3.4.4 Draught

27. Surface draughts are difficult to quote with reasonable accuracy because they vary so much depending on the amount of water and in particular auxiliary ballast water taken from the submerged condition to reach the surface condition and also on the trim. The figures quoted in Appendix IIA are taken from a statement prepared by DNC in 1912. They are mean draughts above keel amidships. The difference between C1-18 and C19-38 is due to the ballast keel fitted from C19 onwards.

Only one figure has been seen for the draught at perpendiculars and that was for the Holland boats of 7ft 6in at the FP and 12ft 10in at the AP with a surface displacement of 113 tons and the vessel trimmed 5° by the stern. In the A2 type, the maximum draught was 12ft 9 in when the main hull was just submerged on a level keel and 14ft 5½in when trimmed 5° by the stern. The boat was then very nearly in the diving or awash condition.

3.4.5 Freeboard

28. In the Holland boats the freeboard was so low that the conning tower hatch had to be closed in the slightest seaway. In the lightest surface condition the freeboard to the top of the conning tower was only 4ft and to the superstructure deck 2ft 3in. The former increased to 6ft 6in later on when the original 2ft conning tower was replaced by one 4ft 6in high.

In A1 the conning tower was made 7ft high with a freeboard of 8ft 10in but there was only 2ft freeboard to the superstructure top.

In A2-4 the conning tower height was reduced to 5ft 6in and a portable bridge fitted at the after side. Because of the latter presumably, no superstructure was fitted amidships. The figures for freeboard became to top of conning tower 7ft 7in, to the bridge 6ft 3in and to the top deck (the pressure hull) 2ft 1in.

In A5-13 the conning tower was increased in height to 6ft 3in, the bridge was raised and a small superstructure fitted aft of the bridge. The freeboard figures increased to 8ft 4 in to top of the conning tower, 7ft 11in to bridge deck and 3ft 2in to the superstructure deck.

In the B Class and C Class, the height of the conning tower was again increased, a better bridge was fitted and a much longer superstructure. The main improvement in freeboard over the later A Class was an increase of 18in or so to the top of the conning tower.

3.4.6 Ballast Keel

29. The first record of a ballast keel having been fitted is for C21 the first of the 1907/08 Programme launched at Vickers in September 1908. This keel was 5½in deep and 2ft 6in wide running from 62-29 Frames, a length of 49½ft. As completed C21 was supposed to carry 12 tons of permanent ballast, 9 tons of which was in the keel. In C22 to C32 the keel was reduced in length to 36ft between Frames 58 and 34. However later boats e.g. C35-38 were fitted as C21. C19 and C20 were also fitted retrospectively as C21 and possibly also the earlier boats of the C class.

3.4.7 Bilge Keels

30. Bilge keels were fitted in the Holland boats over half the length amidships. They were of single plate 9 in. deep on a radius at 49° to the vertical. This practice was retained in all the classes, but reduced to about one-quarter the length of the boat from the A Class onwards. This may be because it was found that they were not so necessary as at first anticipated and the boats did not roll so much as expected. Any saving in weight would have been well worth while.

3.5 Holland Boats Inclining Experiments

Table 3.1 - Holland Boats Inclining Experiments

3.6 A Class Inclining Experiments

Table 3.2 - A Class Inclining Experiments

3.7 C Class Inclining Experiments

Table 3.3 - C Class Inclining Experiments

3.8 Holland Class Displacement and Stability

31. As designed the Holland boats were very sensitive to even small increases in weight. There was little if any permanent ballast to compensate for any weight in excess of the design figures. Before completion one of the two main ballast tanks had to be kept permanently closed to allow for additions by then made and to give some permanent ballast to be used as compensation for future additions. This decrease in main ballast capacity was of course at the expense of reserve of buoyancy and freeboard. Similar limitations were experienced in the later classes.

32. The surface displacement often quoted for these early classes was not the submerged displacement less the main ballast water blown. When submerged the boat had some positive buoyancy (300lb in the Holland Class; 500lb in the A Class and 0.5 tons in the B Class and C Class.) When the main ballast water had been discharged the displacement was the submerged displacement less the main ballast water and less the positive buoyancy. The boat was then in the READY TO DIVE state. This is hereafter taken as the surface displacement and the reserve of buoyancy is calculated on these figures, i.e. the main ballast water plus positive buoyancy submerged divided by the surface displacement. When operating on the surface some auxiliary ballast water was discharged in addition to improve seaworthiness so that normally the displacement was a few tons less than the true surface displacement and is sometimes called the light surface condition.

33. Some typical examples of Inclining Experiments are shown in Tables 3.1, 3.2 and 3.3. The striking feature is the small amount of auxiliary ballast and trimming water available for adjustment. In many cases the full capacity of the main ballast tanks was not used. The permanent ballast, where there was any, was undoubtedly adjusted to allow the main ballast tanks to be fully used but this was not always possible. Restrictions had to be imposed as will be mentioned later.

The figures given for stability in the following paragraphs are typical figures at a particular time in the life of the vessels. They show the trend with age but every effort was undoubtedly made at the time to keep the decrease to a minimum without imposing too many restrictions.

34. In the Holland Class the submerged displacement as built is given as 121.83 tons and the surface displacement as 110.23 tons. This was with only one main ballast tank in use of 9.16 tons capacity and means that about 2.3 tons of auxiliary ballast water was discharged to get to the surface condition quoted, allowing for 300lb of positive buoyancy when submerged.

With a higher conning tower fitted circa 1905-06, the submerged displacement increased to about 122.5 tons and the true surface displacement to about 113.2 tons. It was however the practice to discharge auxiliary ballast water to decrease the displacement to 111/112 tons when operating on the surface.

In the true surface condition at 113 tons displacement the reserve of buoyancy was about 8.2%. At 111 tons light surface displacement it rose to 10.4%.

35. Some interesting figures at various displacements are:

Since the original conning tower was only 24 in high the freeboard to the top of the conning tower in the light surface condition was not more than about 4ft; this increased to 6ft 6in when a higher conning tower was fitted.

The boat on the surface trimmed 5° by the stern with draughts forward 7ft 6in and aft 12ft 10in. Longitudinal stability was small with a longitudinal GM of only about 7ft and considerable change of trim took place with variation in surface speed and also by transfer of water in the boat. Transfer of 0.3 tons of water between the forward and after trimming tanks changed trim by 16in.

36. In 1903 the permanent ballast carried was of the order of 4 tons, yet in 1906/07 it had increased to about 8 tons. This ballast was carried in the original after main ballast tank. The buoyancy of the increased size of conning tower could have made a difference of something less than 1 ton. Where other saving in weight occurred it is difficult to ascertain. A surface GM of 6in and submerged BG of 11in were given originally by Vickers and these are probably as designed. Whatever the as built figures were by 1906-07 they appear to be of the order GM 6.5in to 6.9 in and BG of the order of 9 in. By 1912 DNC was quoting GM6.75in. and BG 8.6in. for the class.

It is interesting to note in Table 3.1 that in the experiments on boats Nos 2 and 4 in May 1906 the main ballast tank capacity was not fully used in the diving condition. Some water was put in the auxiliary ballast tank, to get a trim. The disposition and quantity of permanent ballast was obviously altered after the experiments to allow the full main tank capacity to be used. These experiments were carried out four years after the boats were built and it is remarkable that the stability, both surface and submerged are still very good and there is a reasonable amount of permanent ballast available.

3.9 A, B and C Class Displacement and Stability

37. Although the A Class were larger than the Holland boats, the latter's shortcomings persisted. As built the reserve of buoyancy was slightly better in A1 at 9.2% and also in A2-4 at 8.717% but it was worse in A5-13 at only 8.1%. Once again it appears that all the main ballast tank capacity could not be used. The total capacity of the main tanks in A1, A2-4 and A5-13 was 17.2, 16.2 and 15.2 tons respectively. Yet in the inclining experiments in Table 3.2 the full ballast tank capacity could not be used and no Spare torpedoes were carried and the fuel tanks were not full. In some of the boats adjustment could not be made on permanent ballast and in any case the stability was such as to make this an undesirable thing to do. There is no doubt that by about 1906 there must have been a. restriction on the amount of main ballast water that could be used, a restriction which increased until the reserve of buoyancy became as low as 6.6% in A2-4 and 6.2% in A5-13.

So within a few years of completion most of the boats were in trouble with weight, no spare torpedoes could be carried and, if they were, gasoline had to be reduced. Permanent ballast was running low. In most of the experiments given the full stowage of gasoline (7.0 tons) was not being carried, nor the spare torpedoes.

38. In A1 the submerged displacement was just over 207 tons and in the remainder of the class about 205.5 tons. The surface displacement for the class was about 190 tons.

At 190 tons displacement the freeboard to the top of the pressure hull in A1-4 was about 2ft - no better than in the Holland boats - increased by about 1ft in A5-13. However, the conning tower had been made 7ft high as against 4ft 6in for the Holland, this increased the freeboard to the top of the conning tower.

39. For A1 Vickers gave the surface GM as 8.75in and the submerged BG as 12in. These are probably design figures A1 being the first boat designed by the firm. For A2-13 Vickers quoted GM 6in. and BG 10in. The very reasonable amount of permanent ballast allowed originally had been gradually used up during development and building. By 1907 the stability figures had decreased with the GM below 6in. and the BG below 9 in. In 1912 DNC quoted GM 5.6in. and BG 9.1in. for A1 and GM 5.5in. and BG 8.5in. for A2-13.

40. In the B Class and C Class the main ballast tank capacity was increased over the A Class relative to the size of the boat and the reserve of buoyancy rose to 10.1% and then to 10.4170in C19-38. The stability was less. From the inclining experiment results in Table 3.3 it can be seen that there were restrictions In the use of main tanks, gasoline and fresh water. These restrictions increased over the years until the reserve of buoyancy became as low as 8.7% in the B Class, 7.9% in Cl-18 and 8.3% in C19-38.

Taking the experiment on C14 as an example and this was conducted after being fitted with air traps for escape arrangements and a permanent bridge. The main tank capacity was 28.5 tons. Only 27.0 tons of main ballast water was used and there was little other water ballast on board which could be discarded to allow more main ballast water to be taken in. Again there was a restriction on the use of the main tanks. Although the vessel carried 7.8 tons of permanent ballast the surface stability was so low that it was undoubtedly unwise to decrease the stability further by reducing the permanent ballast to allow the full capacity of main ballast, fresh water and gasoline to be carried.

41. In the B Class and Cl-18 the submerged displacement was 316 tons and the surface displacement originally 287.5 tons increased later to about 289 tons. The design surface GM was of the order of 5in. and the submerged BG about 9 in. These figures soon fell as low as 4.3in and 8.2in for some vessels. In 1912 DNC quoted figures of 4.9 in and 8.8in for the class.

From C19 onwards a ballast keel was fitted and permanent ballast carried in it. This marginally improved stability in both conditions. The submerged displacement increased to 320 tons and the submerged BG rose to nearly 10in. The surface displacement remained very nearly the same as in the earlier boats at 290 tons since the main ballast capacity had been increased. The surface GM rose above 5in. In 1912 DNC quoted the GM as 5in. and the BG as 9.75in. The GM of the B Class in the worst condition, that is the extreme light surface condition, is stated to have been 3.85in.

3.10 Speed and Endurance

42. The first press release on the Holland boats included a statement to the effect that 'the speed laid down is 8 knots in fine weather and 7 knots in ordinary weather. With 160 hp an endurance of 400 miles and surface speed of 9 knots.' Writers at the time mentioned speeds for the Holland varying between 8 and 9 knots. The specification figure was 8 knots. On trials 7.4 knots was obtained.

The Adder Class, built in the USA, were Holland type boats with which the British Holland boats were supposed to be identical. They were certainly of the same size with the same engine horsepower. Sueter gives some records of trials in the USN boats as follows:

• On trials in November 1902 the following results were obtained:

  	Light Surface	'Awash'	Submerged
  Adder, knots	8.732	8.12	7.08
  Mocassin, knots	8.416	7.898	7.224'

  
  It does not state whether these results were 'mean of mean' runs on the measured mile and the inference is that they were not.
• On trials in 1903 in light trim over a ten mile course Pike did 8.55 knots at 230.8 rpm and Grampus 8.47 knots at 227.7 rpm.' These were not 'mean of mean' results.
• On a two mile course submerged, PUCE covered 1.95 miles equivalent to a speed of 7.14 knots at 173.5 mean rpm; 500 amps and 115 volts.' This is very nearly full power. Depth 12ft.

There was a definite difference in the maximum shaft revolutions between the British and American boats although the main engines and motors appear to have been the same. The gearing must have been different. The maximum surface revolutions in the American boats appear to have been about 230 rev/min. In the British boats it was 320 rev/min.

43. The surface speed estimated as likely to be obtained in Holland 1-5 was 8 knots at 150 bhp. In 1912 DNC gave a figure of 7.25 knots at 150 bhp and later 7.5 knots at 160 bhp. Vickers gave 7.4 knots at 160 bhp, probably a trial figure. These speeds were undoubtedly at the light surface displacement.

Vickers state the surface endurance as 236 miles at full speed and 355 miles at half power, figures undoubtedly prepared when the boats were new. Later on a maximum endurance of 235 miles was quoted. The oil fuel consumption for the engine is given as 20 gallons per hour at 160 bhp. Based on this figure and allowing 95% usage of the 600 gallons of gasoline carried the surface endurance at a full speed of 7.4 knots is approximately 210 miles and at half power, say 6 knots, in the region of 310 miles. These are maximum figures when the boats were new. Considerable trouble was experienced with the engines on service and furthermore with age efficiency would decrease and so would endurance. In considering service endurance account must be taken of the fact that the Holland boats would quickly lose both speed and endurance In the slightest weather. Taking all factors into consideration the figure of a maximum endurance of 235 miles may well be a reasonable one after a year or so in service.

44. The submerged speed estimated as possible in the Holland Class was 7 knots at 80 bhp although the motor was designed for a maximum of 70 bhp. They had to run at 5 to 6 knots to be able to submerge and keep control submerged. From the E Class submarines onwards the maximum speed was related to 1 hour duration of battery discharge. In these early boats the duration of battery discharge at full speed is given as 3 hours 45 minutes in the Holland Class and B Class, just over 4 hours in the A Class and 2 hours 20 minutes in the C Class. A higher rate of battery discharge was possible in the B Class and C Class, which increased the bhp and speed. However, because of the high speed which had to be maintained when submerged and the service desirability of having a reasonable time submerged, the duration of battery discharge rates mentioned above were undoubtedly held. Short bursts of higher speed might have been possible if submerged control would allow, but it does not appear to have been a normal service practice or even desirable.

DNC quoted a submerged speed of 6.5 knots at 74 bhp and Vickers a speed of 5 knots only. An Engineer's notebook of the time stated an endurance of 3 hours 30 minutes at 6 knots. Although a reduction in speed with age is to be expected, 5 knots seems to be low in view of the results in the USN boats and the estimated speed of 7 knots. It is probable that the 5 knots was chosen as the constant operational submerged speed based on diving and keeping submerged control, coupled with a reasonable time dived.

The submerged endurance was about 20 miles at 5 knots. This was the maximum and only submerged endurance if the assumption above is correct.

45. For the A Class figures given by various authorities for surface speed in knots at bhp are as follows:

The most consistent figures are given for A5-12 with a speed of say 11.4 knots probably when built and 11 knots after some years service. Based on these, the speed for A2-4 is taken as 10.5 knots when built and 10 knots on service and for A1 as built 10 knots and on service 9.5 knots. For A13, with a 500 hp diesel engine, it is unlikely that she would have the same speed as the 600 hp petrol engined boats and so for this boat the speed is taken as 11 knots. The actual horsepower of the main engines in the various types is discussed in Chapter 25.

The design figure for surface endurance was 600 miles at 11.5 knots. This figure is optimistic. Various figures in miles have been stated as follows:

Vickers state that the fuel consumption figures for A5-12 as they left Barrow were 0. 885lb per bhp hour at full speed and 0.95lb per bhp hour at cruising speed. The figures for endurance for A5-12 given in(c) above agree with these consumption figures. The fuel consumption figures at full power for the other types were of the order of 0.8lb per bhp hour (350 bhp) for A1, 0.93 (450 bhp) for A2-4 and 0.42 (500 bhp diesel) for A13. The corresponding endurance at full power would be approximately 500 miles at 9.5 knots in A1. 360 miles at 10 knots in A2-4 and over 400 miles at 11 knots in A13. The A13 figure is undoubtedly high; the consumption figure is optimistic and unlikely to have been achieved on service.

46. The estimated legend submerged speed was 7 knots at 160 bhp. A figure of 4.5 knots at 80 bhp was also quoted about the same time but it is doubted whether the boats could keep satisfactory control at this speed. It is also doubted whether more than 130 bhp could be developed. Years later the speed for the A Class was give as 6 knots and this is a reasonable figure to take for the class generally in service. For the powers likely to have been obtained see Chapter 26.

The only figure seen for submerged endurance, which is at all within reason, is one by Vickers of 16 miles at full speed. Since the duration of discharge of the batteries at full speed is over four hours the Vickers figure is low at 5 or 6 knots. It was probably 20-24 miles.

47. The design maximum surface speed in the B Class was 13.5 knots although the estimated speed in 1906 was 13 knots. In 1912 it was quoted by DNC as 12 knots whilst CB 1815 gave 12. 5 knots. Vickers gave a speed of 12 knots for all the B Class and C Class boats. Measured mile runs in B1 are given as just over 11.5 knots at 380 rev/min 10.9 knots at 360 rev/min and 9.5 knots at 300 rev/min at a mean draught of 11ft (reserve of buoyancy 28.25 tons) and trimmed 1.5°-2° by the stern. These figures represent 12 knots at full power 400 rev/min which is considered to be the true speed of the B Class as built.

The surface endurance as designed was 1300 miles at 9 knots. In 1912 DNC quoted 1300 miles at 9 knots and 1480 miles at half power and CB 1815 (1914) 1350 miles at 9.5 knots and 950 miles at full speed. There is a mix-up in these figures since they are more relevant to the C Class than the B Class although at the time these two classes with the same dimensions, displacement and power were taken as the same. However the engine fuel consumption when the boats left Barrow was 0.88lb per bhp hour at full speed in the B Class as against 0.715lb per bhp hour in the C Class. At cruising speed the corresponding consumption figures were 0.95 and 0.80.

Vickers gave the endurance of the B Class at full speed (12 knots) as 740 miles and at half power 1100 miles and these are accepted as the maximum possible at these powers.

48. The estimated submerged speed was 7 knots at 210 bhp and speeds varying between 6.5 and 9 knots have been given. The B Class is often quoted as being the same as the C Class but the motor in the former was of 200 ehp as compared with 300 ehp in the latter. Both DNC and Vickers gave a figure of 6.5 knots at 189 bhp. From the results of speed trials in the C Class given in Paragraph 50 it, is certain that a speed of 6.5 knots was never exceeded in the B Class.

Vickers gave the submerged endurance as 16 miles at full speed and DNC during the design stage as 50 miles at 4.5 knots. The former appears to be low at 6.5 knots and was probably 20-22 miles.

3.11 C Class Speed and Endurance

49. As mentioned above, although the C Class were repeats of the B Class in dimensions and engine hp, the fuel consumption in the former was improved. For C1-18 the surface speed remained as in the B Class at 12 knots but the surface endurance increased to 910 miles at full speed and 1360 miles at half power.

The submerged power was increased by 50% over the B Class. Vickers quotes 7.5 knots at 300 hp as the full speed submerged and this appears to be a design figure. DNC in 1912 quoted 7 knots, a more likely figure to have been achieved. Many improvements were made in bigger conning towers, bridges and superstructures, and different types of hydroplanes, all of which tended to reduce submerged speed.

The battery discharge rate at full speed was only 2 hours 20 minutes at 500 amps. so that at 7 knots the endurance would be of the order of 14 miles. An endurance of 50 miles at 4.5 knots is also given, undoubtedly a design figure.

The normal full speed revolutions submerged in the B Class were 280 rev/min but the motor could carry an overload to 300 rev/min. In C1-18 normal revolutions were 275 rev/min but with overload rose to 300 rev/min so that the speed increased, but duration at this speed decreased. Confusion is caused because the speed with overload is often quoted as the normal submerged speed.

50. Towards the end of 1908 various modifications were made to improve both surface and submerged speed in C19 onwards. The tail frames were redesigned and a new design of propeller fitted. Other hull details included in particular the redesign of the engine exhaust pipes. Further improvements affecting the submerged speed were new designs of the conning tower and the fitting of a fixed bridge.

Runs were made in May 1909 on the measured mile at Gareloch with the following results:

'The submerged results were very satisfactory and showed a gain of 1.5 to 2 knots at 294 rev/min over the previous best performance in a C boat. This latter was in C13 after altering the conning tower fairwater similar to that fitted in C22. The C13 results were themselves 0.5 knot better than before this alteration. It must be taken into account that the revolutions at 294 were very high, the normal maximum for the main motors being 275. This was achieved by reducing the duration of battery discharge. At 275 rev/min the speed would have been just over 8 knots.

51. C22 and C24 were completed in March 1909 and the modifications mentioned in Paragraph 50 must have been made during building. The maximum surface speed after the modifications would have been about 13.5 knots at 400 rev/min when trimmed 0.5° bows up. Increase in trim by the stern had a slight effect on speed, e.g. at 1.5° bows up the loss was about 0.3 knots. The designed trim was 1° by the stern.

Vickers gave a speed of 12 knots for C21 onwards the same as for C1-18. DNC in 1912 does allow an increase to 12.5 knots and Watts in 1919 and CB 1815 (1914) gave 13 knots. From the statement made in Paragraph 50 that 'these surface speeds were reached at much lower revolutions than previously' it appears that the modifications gave an increase in speed of slightly more than 1 knot. It is fair to assume that as built C19-38 had a surface speed of at least 13 knots.

Normally the improved speed for the same power would have increased surface endurance but the fuel carried in C19-38 was about 10% less than in Cl-18 and the endurance therefore remained about the same.

The trial figure in Paragraph 50 for submerged speed of 8.6 knots at 294 rev/min is equivalent to about 8.1 knots at the normal 275 rev/min Vickers gave the speed of C19-38 as 8 knots and DNC in 1912 at 8.5 knots. This conforms with the statement made regarding the improvement in speed over previous boats and with a speed of 7 knots in C1-18. The speed for C19-38in service is taken as 8 knots.

The duration of discharge of the battery at full speed was only 2 hours 20 minutes and therefore the submerged endurance at full speed was of the order of 16 miles. The design endurance was 55 miles at 5 knots.

Because of the benefits achieved by the modifications in C19 onwards it is to be expected that the earlier C boats were also modified retrospectively.

52. All these classes trimmed by the stern on the surface the angle being greater the smaller the vessel. They were very sensitive to trim with increase in speed and turning. Trials in B1 showed that putting the helm either way brought the bows up by as much as 3° and this same angle was achieved by putting the after diving rudders (hydroplanes) hard up. It appeared to be a common practice to use the after planes to bring up the bows when running on the surface.

The surface turning circle of B1 was about 130 yards (approx 3 lengths).

53. So many factors affect speed and endurance that it is difficult to analyse quoted figures. However, the details given in Appendix IIA are considered to be reasonable and give a good comparison between the classes. Details of the main engines of these classes are given in Chapter 25 and Appendix VIA and of the main motors and batteries inChapter 26 and Appendix VIIA.

3.12 Structure

54. No specifications or structural drawings have been seen for these boats except the B Class construction sections shown in Plate 6: . The sizes of the pressure hull plating and the main frames of the various classes were however available from Vickers' records. Sueter states that the Holland boats were built to the specification for Holland Boat No 10, that is the USN Holland No 3 (Adder Class), and gives details undoubtedly from the specification. Comparing these details with Plate 6: it is considered that the same type of structure and scantlings was used throughout the classes, except for an increase in thickness of pressure hull plating in the later boats of larger diameter. In connection with the actual structure therefore the description below applies to the B Class and differences in the Holland Class, A Class and C Class will be mentioned where known.

55. The pressure hull amidships was worked in eight strakes of plating with inner and outer strakes as shown in Plate 6: except that the plate at the top of the pressure hull was probably flattened in the middle to touch the frame line. The number of strakes would decrease towards the ends of the boat and the thickness.

In the Holland boats, 17½lb plating was used, although Sueter states the plating at the ends was decreased to 14 lb. A1-4 were similarly plated except that the inner strakes amidships were 20 lb. A5-13 were similar to A1-4 except that all plating amidships might have been 20lb as it was in the B Class and C Class. The forward and after ends of the pressure hull were castings.

56. The main frames of 3½in x 3in x 7.8lb angle bars were spaced 18in apart reduced to 3½in x 3in x 6.6lb angles at the ends. The 18in frame spacing was practically constant and where it had to be varied for some local reason, which was seldom, the variation was corrected in adjoining frames, for example in the Holland boats frames 30-31 were 17in apart and frame 31-32 were 19in apart.

An interesting point in Plate 6: is the mention of a 'welded' frame in the engine room. Whatever the 'welding' was the connection involved was undoubtedly for a portable section for shipping the machinery.

57. No internal main watertight bulkheads were fitted in any of these classes so that they were all one-compartment vessels.

When C6 was re-trimmed on 15 November 1912 it was stated that the vessel was 'now fitted with bow hydroplanes and a collision bulkhead'. C6 was completed in January 1907. This suggests that all the C Class at some time after completion were fitted with a watertight bulkhead forward as in the D Class, see Plate 9, to form additional protection in the event of damage to the bow in collision. The compartment so formed was called the Collision Compartment. It could be that this collision bulkhead was fitted retrospectively in the B Class.

58. The general pattern of decks was for the tank tops forward and aft of the batteries to extend the width of the boat. In way of the batteries, the tanks extended under the bottom and round the sides of the battery tanks with the tank top just below the top of the battery tanks. Manholes were fitted in the pressure hull at the bottom of the main ballast, buoyancy and gasoline tanks and also inboard for access to all tanks.

59. A rectangular flat plate torpedo hatch about 6ft x 1ft 7in was fitted forward for embarking torpedoes in the Holland Class. It was on a 3in coaming on the pressure hull. The torpedoes were embarked tail first going aft by crane from shore or another ship since no torpedo derrick was fitted on board.

The only other access to the boat was through the conning tower hatch. Originally there was no lower conning tower hatch but one was fitted retrospectively at least in the A Class onwards and became standard practice thereafter.

This arrangement of hatches applied to all the classes. In A5-12 onwards a portable crane was carried for embarking torpedoes. The crane was probably supplied to the earlier A boats but it is unlikely it was ever installed in the Holland's.

60. The American specification for the Holland boats stated that the 'whole structure was tested to withstand a crushing pressure of 100 feet of water corresponding to 43.5 pounds per square inch pressure'. Whether this meant that the submarine as a whole was actually tested to this pressure externally in America is not known but it is unlikely to have been done in this country. A record has been seen that in C12-16 the shell was tested by filling the boat with water and applying a pressure of 35lb/in². This was the common practice for testing the hull internally but is very different from applying an external pressure to simulate conditions when dived. Tanks were tested as follows:

• 50lb - Trimming Tanks; WRT's; Collision Compartment; Main Ballast Tanks; Spare and Auxiliary Tanks; Statical Diving Tank; Lead Ballast Compartments.
• 25lb - Gasoline Tanks and Water Jackets round Gasoline; Compensating Tanks; Lubricating Oil Tanks.
• 35lb - Conning Tower.
• 95lb - Firing Tanks.

61. A small horizontal superstructure was fitted in the Holland's for about half the length of the boat amidships and then sloping downwards to the forward and after ends. It was 4ft 5in wide and only about 3in above the pressure hull amidships. This superstructure was the bridge deck for personnel when operating on the surface. It had a towing slip forward mooring cleats each side and a locker for stowing the anchor and cable. The conning tower was only 2ft high and the coxswain sat on the edge of the conning tower to operate the steering wheel.

This was a very simple structure and the freeboard was small and in any weather the conning tower hatch had to be kept closed. The conditions for personnel on top must have been very bad. It was obvious that bigger and better arrangements were required in the classes that followed. Even within the space of a couple of years or so there were larger and higher conning towers faired in by plating, and a bridge.

The trouble in these early boats was the heavy bow wave which built up forward when underway on the surface. This, coupled with low longitudinal stability, tended to make the vessels plunge. Efforts to improve this were made by increasing the size of the superstructure right forward. The USN was taking similar action. The introduction of bow hydroplanes and firing tanks in the forward superstructure and capstans and cable holders of necessity made the forward casing much larger in the later C boats. However, additional superstructure meant added weight and loss of stability and both were at a premium. Some calculations have been seen 'to find the effect of removing the cork packing and some of the superstructure abaft the conning tower in C21-30'. These calculations were made on Admiralty instructions early in 1908 either before the boats were laid down or immediately afterwards. There is no doubt about the beneficial effect of having cork in the superstructure to increase buoyancy and ballast but whether it was ever fitted in any boats either before or after these calculations is not known. However, in the C Class no superstructure was fitted over the after 40ft of the boat to save weight.

Outlines of the superstructure in each class and some details are shown in Plates 1-8.

62. Details of hull items such as conning towers, bridges, rudders, hydroplanes, etc are given in Chapter 20, Chapter 21 & Chapter 22.

3.13 Arrangement of Tanks

63. The arrangement of tanks in the Holland boats consisted of:

Forward Trimming Tank	- Extreme forward end
Compensating Tank (AWRY)	- Under fore end of torpedo tube
Gasoline Tank	- Under after end of torpedo tube
Main Ballast Tank No 1	- Under forward battery
Auxiliary Ballast Tank	- Under after battery
Buoyancy Tank	- Amidships
After Trimming Tank	- Extreme after end

For tests applied see Paragraph 60.

The number of tanks and compartments tested was ten; with development in design the number tested increased to twenty-nine in the C Class. The sequence of changes and growth of the various named tanks follows in some detail because, by the end of the C Class, a general pattern for internal tanks had been established.

Details of tank capacities in all classes are given in Appendix IVA and of the flooding, venting, pumping and blowing arrangements in Chapter 23.

Typical arrangements of tanks are shown in:

• Fig 3.4: A2-4 Arrangement of Tanks
• Fig 3.5: A5-12 Arrangement of Tanks
• Fig 3.6: B2-11 Arrangement of Tanks
• Fig 3.7: C21-30 Arrangement of WT Compartments

3.13.1 Main Ballast Tanks

64. As designed the Holland boats had two main tanks, one just forward of and the other just abaft amidships, under and at the sides of the battery tank, with a total capacity of about 15 tons. The tanks had flat tops and inboard sides and although tested to 50lb/in² the structure was of reasonably light construction and the Kingstons had to be kept shut when diving below periscope depth. Before completion it was found that the after tank could not be used for main ballast. The boats therefore for all their service lives had only one main ballast tank of just over 9 tons capacity. This unfortunately decreased the reserve of buoyancy from 13.4% as designed to only 8.2%.

The one main tank was flooded from the sea through two 7in Kingstons, had a 2in suction from the main line, one 3in vent each side led directly outboard, and was blown by air at 10lb/in².

65. The Holland boat arrangement as designed was fitted in A1, two tanks under and at the sides of the battery tank, with an increased capacity of about 17.2 tons. However before very long a restriction had to be placed on the useable main tank capacity. The forward tank was about 18ft long and very shallow. 'With completely unrestricted flow it would take about one minute to flood.' In practice it must have taken much longer with an adverse effect on the time taken to dive.

In A2-4 this forward tank was subdivided into three separate tanks making four main ballast tanks in all, each with its own Kingston and flooding and blowing arrangements. In addition the whole of the block in way of the battery tank was rearranged and in the process the main tank capacity was reduced to 16.2 tons. This retrograde step must have been forced upon the designers to obtain more auxiliary ballast water.

In A5-13 this block of tanks was again modified and the main tank capacity fell to 15.2 tons and the reserve of buoyancy became less than in the Holland boats. In spite of this reduction in main ballast water it was necessary to restrict the use of the full main tank capacity in all boats of the A Class after a few years in service.

From A2 onwards the Kingstons were fitted in small WT compartments on top of the tanks and large tail pipes led to the bottom of the tanks. Although this made all working parts of the Kingstons accessible it must have increased the flooding time.

A2-13 had a tank immediately aft of No 4 main ballast tank which was called a spare tank or ballast tank (1.0 ton capacity) and was supposed to be used for main ballast water if necessary although it had no Kingston or lead from the auxiliary 50 lb/in² air system but could be flooded from the main line. This tank has been named on some drawings as 'No 5 Main Ballast Tank', but it is not a main ballast tank in the true sense.

66. In the B Class the number of tanks was increased to six, Nos 1-5 amidships in way of the battery and No 6 aft in the engine room. The total capacity was increased to 28.5 tons. C1-18 were as the B Class except that No 6 tank was moved to the amidships block, retaining the same total capacity. In C19-38 the total capacity was increased to 29.8 tons by extending No 2 main tank to include a spare tank fitted in the earlier boats.

67. A report has been seen dated November 1913 which stated 'that in the early boats and definitely in the A Class and C Class No 6 main ballast was never filled on diving, but only used for trimming when running on the surface.' It also implied that 'in A8 this tank was inadvertently opened when diving and she was lost.' The reference to A Class No 6 main ballast is an error and should be A Class No 4 since they were built with only four main tanks. It is considered that any restriction, which applied to the C Class, would apply to the B Class.

There is no doubt that when C18 and C35 were inclined in November 1913, C35 could use only five main tanks and No 6 was locked empty. In the C18 experiment Nos. 1, 2, 3, 4 and 6 main tanks were filled and No 5 only to the lower pet-cock. In C31, 32, 35-38 the Kingston to No 6 tank of 5.5 tons capacity 'was locked and the tank used as an auxiliary.' This restriction undoubtedly had to be applied to all boats of the class.

The arrangement for flooding and blowing individual main tanks remained the same in the A Class, B Class and C Class as described for the Holland boats.

3.13.2 Buoyancy Tank

68. In all classes a tank named variously the circular tank, the compensating tank, the buoyancy tank and the statical diving tank was fitted amidships. Its centre of gravity coincided with the fore and aft position of the submerged centre of buoyancy. In the Holland Class the buoyancy tank was specially built of cylindrical shape with a capacity of 0.33 tons and fitted inside the auxiliary ballast tank. From A1 onwards it was built-in as part of the structure and strong enough to enable the Kingston to be opened at any depth. The capacity increased with size of the class until about 1 ton capacity in the B Class and C Class. It was used to compensate for changes in seawater density.

Flooded direct from the sea through a 9 in Kingston hand operated from the flat over in the Holland boats, it was fitted with a 1½in suction from the main line and blown from the HP air line through a reducing valve at 10lb/in² pressure. At this pressure it could not, of course, be blown at depth. However, the reducing valve could be by-passed for increasing the blowing pressure as required. In A1 the size of the Kingston was reduced to 3½in and the main line suction increased from 1½in to 2in. From A2 onwards the, Kingston was deleted and a probable reason for this is given in Chapter 18, Paragraph 15.

3.13.3 Auxiliary Ballast Tanks

69. The after main ballast tank in the Holland boats as designed could not be used as such. It was thereafter called an auxiliary ballast tank, had a capacity of about 4.5 tons and was sited amidships. It was fitted with a 3½in. Kingston operated from the control room, a 1in vent, two 2in main line suctions and leads from the HP air system for blowing at 10lb/in². It is stated that by means of this tank and the forward trimming tank it was possible to compensate for the full stowage of gasoline of 1.9 tons. For a normal diving trim the auxiliary ballast tank was ideally kept between one half and three quarters full. This water was usually discharged after surfacing to increase freeboard and seaworthiness. Any permanent ballast was as far as possible stowed in this tank.

70. In A1 a second auxiliary ballast tank (2 tons) was fitted at the after end since additional fuel was carried. The total tank capacity for auxiliary ballast only increased to 5.2 tons in spite of having over 7 tons of gasoline alone on board. The only other tanks for carrying compensating water were the trimming tanks with a total capacity of 1.25 tons. The fuel tanks were not of course self-compensating. Appendix IVA this second auxiliary ballast tank is shown as a fuel compensating tank.

It was realised that tankage for compensating water was low in A1. In A2-12 the same amount of fuel was carried as in A1. A gasoline compensating tank was fitted adjacent to the after fuel stowage, two auxiliary ballast tanks amidships and an adjusting tank in the engine room. The tank capacity of 5 tons in A1 was increased to 8.5 tons in A2-4 and 9.5 tons in A5-12. In A13, fitted with a diesel, the compensating and adjusting tanks in the engine room were removed when the after fuel stowage had to be forfeited. The auxiliary ballast capacity decreased to 5.6 tons but the fuel carried had also decreased by 3 tons.

71. In the B Class and C Class the gasoline carried increased to 15.5 tons. Three auxiliary ballast, two fuel compensating, two adjusting and two spare tanks, nine tanks in C1 with a total capacity of about 23 tons, were fitted in the B Class and C1-11. The increase in tank capacity to 23 tons from the 9.5 tons in A5-12 was rather excessive as was the number of tanks but was probably an insurance against problems experienced in the earlier boats. C12 was not started until after C1 had completed and C12-18 had 22 tons in eight tanks. Similarly C19 started to build after C12 was in service and C19-38 had 18 tons of water in six tanks. In the latter the weight of oil fuel, lubricating oil, fresh water and provisions which had to be compensated was about 17 tons.

The pumping and flooding arrangements in the A Class, B Class and C Class were of the same pattern as in the Holland except that the Kingstons were not fitted.

3.13.4 Trimming Tanks

72. For correcting changes in trim, forward and after trimming tanks were fitted in all classes, one in the bows and the other right aft. in the Holland's the total capacity of the two tanks was just over 1 ton; it increased slightly in the A Class but was only 1.18 tons in the B Class and C Class.

Normally, these tanks were kept about half full as far as possible. A 1½in trimming line ran fore and aft connecting the trimming tanks, with a cross connection to the main line amidships. Water could be blown from one tank to the other by HP air at 50lb/in². All operations were controlled centrally by valves in the control room.

3.13.5 Gasoline Tanks and Fuel Compensating Tanks

73. A single gasoline tank of about 1.9 tons was built under the torpedo tube forward in the Holland boats. No special compensating water tank was provided; the forward trimming tank and the auxiliary ballast tank were used for this purpose. The call for greater endurance meant increased gasoline stowage and in A1 an additional tank was fitted giving a total capacity of gasoline on board of 7 tons. The only tanks available in the boat to take fuel compensating water were the auxiliary ballast and trimming tanks with a total capacity of 6.4 tons.

74. The same arrangement as in A1 was fitted in A2-12 but the hazards involved in carrying and using gasoline were by now appreciated and efforts made to reduce them. The fuel tanks were surrounded, except in way of the pressure hull, by 'jackets' or spaces containing about 2 tons of water. This was expensive in weight but was undoubtedly done to prevent the danger from, gasoline leaking into the boat. In addition a fuel compensating tank of 2.8 tons capacity was fitted next to the after tank for compensating the after gasoline. The arrangement of using the forward trimming tank and the amidships auxiliary ballast continued for compensating the forward gasoline.

The rules concerning the use of the gasoline water jackets are somewhat obscure. Studying the inclining experiments in Tables 3.2 and 3.3 it is seen that the water jackets were usually empty even though the fuel tanks were full. In fact it would have been impossible to fill these water jackets in the conditions mentioned with a full capacity of fuel. Yet on the other hand pipes were fitted for flooding the water jackets direct from the sea and a lead was fitted from the auxiliary 50lb/in² air system. There is a possibility that the water jackets were empty submerged when the gasoline was not being used and full on the surface. This is considered in more detail in Chapter 25.

In A13, because of the increase in weight of the diesel engine, the after fuel tank with its water jacket, the after fuel compensating tank and the after adjusting tank all had to be omitted. The total fuel carried was approximately 3.7 tons of diesel oil.

75. The B Class carried 15.5 tons of gasoline in two tanks, one forward and one aft; with surrounding water jackets and with gasoline compensating tanks forward and aft. C1-11 had similar arrangements. In C12-18 the term gasoline compensating tank was dropped and the term compensating tank adopted for general compensation. In C19-38 the fuel capacity was reduced to 14 tons and this seems to have been accepted by a change of engine from to twelve cylinders with improved efficiency. See Note (3) Appendix IVA.

In all classes a HP line was fitted from the 50lb/in² auxiliary HP service to the gasoline tanks and water jackets spaces (where fitted).

3.13.6 Water Round Torpedo (WRT), Firing and Torpedo Compensating Tanks

76. The WRT and torpedo compensating tanks were used for compensating with water, the changes in weight in the boat after firing torpedoes and changes in fore and aft trim of the boat in bringing reloads to the torpedo tubes. The firing tanks were usually built-in structures which years later became the HP air firing columns.

In the Holland boats the WRT tank is called the compensating tank and sometimes drain tank and was built under the torpedo tube at the extreme forward end. It had a capacity of 0.34 tons. This drain tank operated in conjunction with two compensating tanks of capacity approx 0.2 tons sited at the after end of the tube. Further torpedo compensating tanks of approximately 0.25 tons capacity each were sited in pairs one pair abaft the end of the tube and the other aft of the conning tower to compensate for moving the spare torpedoes from their stowages into the torpedo tube. A torpedo firing tank of capacity approximately 0.6 tons was fitted over the after end of the tube with a firing tank reservoir of about 0.2 tons nearby.

The term WRT tank is used for the first time in A2. The arrangement of the various tanks varied between and within the classes and are given in detail in Chapter 27.

3.13.7 Lead Ballast Compartments

77. In the Holland boats permanent ballast was stowed in the auxiliary ballast tank and in the A Class dispersed through the boat as necessary. In the B Class two small tanks one forward and one aft were allocated for stowing permanent ballast. This practice was also used in C1-18 but was dropped in C19-38 because a ballast keel into which ballast could be built had now been adopted.

3.13.8 Engine Oil Tanks

78. A built-in tank for engine oil is first shown in B2-11. It was for cylinder oil and had a capacity of 0.67 tons and was in the engine room. This tank continued in the same place throughout the C Class. A second lubricating oil tank is first shown in C12 of 0.83 tons. Both these tanks were eventually fitted in all the B Class and C Class boats. In the Holland and the A boats engine oil was carried in ready-use tanks, 0.25 tons in the Holland's and 0.75 tons in the A Class. In A13 a built-in tank, in the engine room was for cylinder oil and a lubricating ready use oil tank was at the forward end between the torpedo tubes.

3.13.9 Fresh Water Tanks

79. As completed the Holland Class, B Class and B Class carried fresh water in ready use tanks. The capacity in the Holland boats was originally 0.1 tons.

In 1909 the need for improved arrangements for fresh water was considered and it is stated that 'built-in fresh water tanks were fitted in C19 and also that a small hand pump with a capacity of 1/3rd pint per stroke was fitted in C8, C17 and C18.'

A D284 for C17 states that '2 tons of fresh water was carried.' It appears therefore that in the later boats of the C Class fresh water tanks were built-in before completion and similar tanks fitted retrospectively in the earlier C boats and probably B Class.

80. Probably in the Holland boats but certainly from A1 onwards all tanks including main ballast tanks were fitted with ¾in. test cocks at the top of the tank, operated locally to check when the tanks were full. From A5, ¾in. pipes were led from the main ballast tanks to cocks at a central position near the blowing panels and the tanks were checked at this position. At some later date additional petcocks at intermediate tank capacities must have been fitted, since a lower petcock is mentioned in the inclining experiment on C18 in Paragraph 67.

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