Home - Dits & Bits - BR3043 - Part Two - Chapter 22

Chapter 22: Conning Towers, Bridges and Periscopes

1. Conning towers, bridges and periscopes developed individually in the early boats but they became very interdependent with the growth in size of submarines. The need for larger bridges for seaworthiness and the protection and efficiency of bridge personnel, the need for longer periscopes to increase manoeuvrability and safety at periscope depth, and increased W/T arrangements. The need to keep silhouette to a minimum became important. The general desire to increase the length of periscopes was in conflict with the need to be able to dive in shallow water. As a result in later boats the design of bridges was a compromise.

22.1 Conning Towers and Bridges

2. The conning tower first fitted in the Holland boats was a 4in thick nickel steel trunk of 2ft internal diameter and about 2ft high with a WT access hatch at the top. This hatch was balanced and opened aft. When closed, it fitted flush into a recess in the top of the trunk, to a depth of 3in or more. It is not known what fastening arrangements were fitted but in the American boats the hatch was made watertight against a rubber gasket by a toggle-locking device. The top of the conning tower was about 8½ft above the control room deck.

A conning tower stand was fixed to the control room flat under the conning tower. Its height was about 27in and could be adjusted. This could have been used to assist in getting out of the conning tower hatch and by the helmsman when operating the lower steering wheel, which was more than 5ft at centre above the deck. See Chapter 21 Paragraph 3

3. Even in the lightest surface condition the freeboard to the top of the conning tower was not more than 4ft. There was no bridge structure; personnel 'up top' stood on the casing which was just over 2ft above the waterline and the coxswain sat on the edge of the conning tower when steering. The arrangement first fitted is shown in Plate 1. This was changed later as mentioned in Paragraph 6.

4. When the first submarines reached Portsmouth after completion it, was obvious that they were too small to work in bad weather and in particular due to their low freeboard the conning tower hatch had to be shut in the slightest seaway. In the A boats being designed before the last Hollands were completed it was decided to increase the size of the conning tower and so increase the freeboard on the surface to over 8ft. The conning tower in A1 was in the form of a truncated cone of 15lb steel plating with a gunmetal hood and cover. It was 4ft 3in diameter at the base, 2ft 11in diameter at the top and 7ft high. Access was through a balanced 19in diameter circular hatch in the after portion of the top, which allowed the periscope to be sited within the conning tower forward of the hatch. A2-13 were fitted with conning towers similar to that in A1, except that it was only about 5ft 6in high in A2-4.

5. The First British Sub Ever To Be Lost At Sea, A1 was sunk off the Nab in collision with SS Berwick Castle on 18 March 1904 and was salvaged on 18 April 1904. Bacon states that:

She had been struck by the ship and the conning tower hatch sprung open slightly, the structure was otherwise undamaged. The boat then travelled the whole length under the ship's bottom during which time sufficient water had leaked in to prevent the boat surfacing.

This collision led to the adoption of a watertight hatch at the bottom of the conning tower. The advantage of this hatch was fully demonstrated when A9 was rammed in February 1906 by the steamer Coath off Penlee Point, Plymouth and managed to surface after the conning tower had been flooded. A5-13 were built with a sliding shutter worked by handwheel through a rack and pinion to cover the hull access opening. A2-4 were fitted retrospectively. The extra weight Involved was 8cwt.

6. About 1905 the conning towers in the Holland boats were replaced by the truncated cone type fitted in A1 except that it was 4ft 6in high only. Access to the pressure hull was through a 27in x 22in rectangular opening closed by a hand operated 22½lb sliding watertight shutter.

7. The truncated cone type of conning towers were fitted with five scuttles (for light) in the hood. In 1911 they were replaced by five 5in x 2in rectangular side scuttles with deadlights and clips.

8. Towards the end of 1904 a small bridge was built in A2-4, see Plate 3. It was abaft and below the top of the conning tower and consisted of a 10lb plate platform supported on pillars, the whole of which was collapsible and stowed on the hull when the boat submerged. The upper steering wheel was at the fore end of this bridge and the wheel and shafting outside the pressure hull was removed for diving.

9. In A5-13 the bridge was raised to the level of the top of the conning tower, see Plate 04. This general arrangement persisted throughout the B Class and up to C18 with freeboard to the top of the conning tower remaining at about 10ft. Very little change had been made in the dimensions of the conning tower from A1. The one periscope ran through the conning tower.

In C1-18 a second periscope was fitted immediately aft of the conning tower and periscope brackets appeared for the first time. The bridge was still portable.

The statements made so far cover the various arrangements expected to be fitted in at least the leading boats of a class or part class. Changes were being made so rapidly that new ideas were undoubtedly fitted in other boats of any class building at the same time or fitted retrospectively in boats completed as soon as possible.

10. This was all leading up to C19 fitted with a fixed bridge. The periscope through the conning tower was deleted and the conning tower was made an access trunk 3ft diameter at the bottom, 2ft diameter at the top and about 7ft high. The conning tower hatch hinged sideways to port and the lower hatch in lieu of a sliding shutter was hinged to starboard and operated by a long handle in the control room. The one periscope only was on the after side of the conning tower. A large fairing of streamline shape enclosed the conning tower which formed the nose of the fairing. The top of this fairing formed the bridge deck. See Plate 8. It is probable that the tops of the ventilators and the steering wheel and shafting above the bridge deck were removed for diving. It is noticed for the first time that engine telegraph and steering indicator shafting is led to the bridge. This can undoubtedly be said to be the beginning of the modern bridge in submarines.

C19 has been taken as being the first submarine to be so fitted during building since she was the beginning of a new program. C21 was certainly built with this bridge whilst C14 was fitted retrospectively early in 1909.


11. The same type of fixed bridge was fitted in D1 but the bridge steering wheel was a fixture and the ventilators hinged into the superstructure. In D2 the fixed bridge was made larger and even larger again in D3-8. Two large periscope brackets extended 7ft above the bridge deck. Even two large firing tanks 8½ft high were fitted in the bridge structure. In spite of this rather excessive use of weight and space, the bridge was only fitted with guard rails and wires presumably covered with canvas. Freeboard to the bridge deck had risen to 12ft and to the superstructure over 6ft.

12. In E1 the conning tower was enlarged to form a steering position in addition to the bridge and control room positions. Periscope brackets were attached to the forward and after sides of the tower casting. The large size of the D Class bridges persisted. In the later boats of the E Class the overall size was cut back presumably because the war had brought home the fact that silhouette was of importance and the smaller it was the better. The reduction was however not of great significance.

13. Without going into details of the changes from the E boats to the Rainbow Class the actual difference between these two classes in principle is small. The E Class had a reasonably large conning tower with upper and lower hatches closed by hand. The two periscopes were fitted one forward and one aft of the conning tower with periscope brackets connected to the tower. A reasonable bridge with the steering wheel at the fore end and a WT mast at the after end. The whole structure was streamlined. The main difference was the lack of protection from the weather to bridge personnel.

14. The upper deck structure in the K Class by the necessity for funnels etc was large. They were high speed Fleet submarines and the protection of bridge personnel was important. This class was therefore fitted with a deckhouse built over and around the conning tower. It was in fact a fully enclosed bridge. This was the first time any protection had been given to bridge personnel in RN submarines other than by canvas screens. In K26 in addition, an open bridge with fixed side plating was fitted on top of the closed bridge. The open versus closed bridge controversy, which later on persisted for so many years in surface ships, has here started in submarines. The enclosed bridge was not repeated in submarines but better protection to the open bridges was provided by fixed side plating and eventually canopies at the forward end. In the Odin and Parthian Class considerable attention was paid to the bridge cab arrangements and modifications were made primarily to improve navigational facilities and not from the aspect of submerged speed. By this time additions in the bridge structure included the Captain's cabin and an upper deck galley. Such additions were only possible of course in the larger types of submarines. In X1 the very large bridge was dictated by the gunnery control arrangements.

22. 2 Compasses

15. In the Holland boats a magnetic compass was sited outboard on the hull abaft the bridge and a 'compass periscope tube' went from this compass through at least two right-angled bends to a position in the control room near the periscope training gear and periscope steering gear handwheels. This arrangement continued in the A Class, B Class and C Class and in the D Class except that the magnetic compass was sited on the pressure hull inside the casing.

It is also stated that 'a duplicate compass was fitted Inside the hull and that the compass on the casing was fitted with a reflecting tube for observation from within the conning tower'. The latter arrangement undoubtedly started when the periscope position was in the conning tower. The duplicate compass would have been a portable binnacle to be used on the bridge.

16. These magnetic compasses were a great trouble owing to the difficulty of screening from electric motors. The Submarine Committee in 1912 stated that 'the need was felt for more accurate navigation submerged for safety in exercises' and put up the gyro-compass as a solution. It considered the provision of such a compass in all future submarines of the overseas type absolutely necessary. Two types-the Anschutz and the Sperry were tried and the latter preferred. It is not known for certain which class first got a gyro-compass but Reference (6) in 1914 mentions Swordfish. They were undoubtedly fitted in most boats from 1914 onwards, the E Class being the first boats in service with a gyro.

17. The projector binnacle eventually evolved. The RL7 type made by Messrs Kelvin, Bottomley and Baird for the Parthian Class cost £563 (estimated) per set. They also carried a Pattern 184 standard compass for emergency.

22. 3 Periscopes

Sir Howard Grubb (1844-1931) designer of the first practical periscope
Sir Howard Grubb (1844-1931) designer of the first practical periscope

18. No instrument which could really be called a periscope was available in 1900. The USN Adder carrying out her official trials in 1902 'used a periscope temporarily rigged through the port forward ventilator - it was fixed and had a field of view of but 15° on each bow'. Reference (8) states that 'while Hajen was being built (1903-05) the first periscopes began to make their appearance. One of these, manufactured by the firm of Officine Galileo in Florence was installed in Hajen before delivery instead of a sighting instrument which had already been purchased'. When Holland Nos 1-5 started to build there was really no periscope available to fit in the boats. However, thanks to Captain Bacon, periscopes were made available. Fig 22.1 is a print of the original tracing prepared by Vickers, Sons & Maxim dated 16 August 1901 of the 'Arrangement of Captain Bacon's Periscope to be fitted to submarine boat No 280'. Boat No 280 was Holland No 1. It is understood that Captain Bacon developed the idea in conjunction with Howard Grubb.

19. The periscope fitted in Holland No 1 was a development of the original arrange­ment show nin Fig 22.1 using the same principle and is shown in Plate 1. The periscope was stowed on the hull alongside the conning tower and was rotated from the horizontal to the vertical and vice versa about a ball joint by hand. The centre of the periscope was about 3ft abaft the conning tower and 1½ft to starboard of the middle line. The eyepiece was obviously fitted after the periscope had been raised. It was trained by hand with the training gear handwheel near to the periscope eyepiece.

This periscope was called a Unifocal Ball Joint Type. Vickers state that the length from eyepiece to headpiece was 21 ft and that the external diameter of me main tube was 3⅜ in. and of the upper tube 2¼ in. Similar arrangements were fitted in the other boats of the class except that In Holland No 2 electric drive for training was fitted as described in Paragraph 21 for A1 and this was probably the prototype gear.

20. When the new truncated cone type of conning tower was fitted to the Holland boats in 1905 the periscope was changed to the type fitted in A1 with the periscope sited to pass through the conning tower. It is stated to have been 13ft long but it was probably the same length as in A1. 'When it was lowered it came to the top of the battery covers with the upper end about 2ft 6in above the top of the conning tower'. These figures are consistent with the new 4ft 6in, high conning tower but by this time a sliding watertight shutter had been fitted at the base of the tower so the maximum travel of the periscope would have been limited at sea to about 3ft.

Fig 22.1
Fig 22.1
Fig 22.2
Fig 22.2

21. In A1 the single 4in unifocal periscope passed through the conning tower and slid up and down two guide rails. Fig 22.2 is a copy of an arrangement for A1 which shows the principles involved. One guide rail could be turned by a small ½hp electric motor (140 rev/min), originally through a belt and pulley but later by means of a worm and worm wheel. A gear wheel, which slid up and down a keyway in this guide, engaged with a gear wheel on the periscope and so turned the periscope. A hand crank was also provided for manual training. The periscope was raised and lowered by a single steel wire pendant passing over a sheave at the top of the conning tower to a screw driven by a ½hp motor. It was supported on ball races at the top and bottom of the guide bracket. The periscope had a travel of 5ft.

The arrangements actually fitted in the A boats are shown in Plate 2, Plate 3 and Plate 4. A1-4 were built without a lower hatch at the base of the conning tower and there was therefore no need to keep all the periscope operating mechanism within the conning tower. The various arrangements differed in detail from those shown in Fig 22.2.

22. A1 had a 4in diameter 12ft 9in long unifocal periscope which was trained by a ½hp motor through a worm gear as shown in Fig 22.2. It was elevated by a screw driven by a ½hp motor, see Plate 2. The screw extended from near the control room deck to the top of the conning tower so that the periscope could be lowered nearly to the battery top. It was as a result of A1 being sunk in collision in 1904 that a lower conning tower hatch was fitted. Although raised after the accident, it is not known whether the conning tower and periscope arrangements were modified in this boat. The periscope was made of 5in brass tube.

23. A2-4 had a 9ft long 4in unifocal periscope and although the lower conning tower hatch was not fitted during building the periscope operating gear was concentrated in the conning tower. The periscope was trained by a ½hp motor through a flexible shaft and elevated by chain using a 2hp motor. A5-13 were similar except that the periscope was bifocal and 8 ft 9in long. Although the periscope could be lowered below the lower hatch as shown in Plate 3 and Plate 4 this would have been the surface position. When submerged it is assumed that the periscope would always be in the raised position with the captain or look out in the conning tower so that the lower hatch could be shut immediately.

24. From A2 to the C Class, there was no set pattern and the type of periscope changed from unifocal through bifocal to stereoscopic. The one 4in bifocal periscope in the B Class was 9ft 6in. long had a travel of 4ft 2in. and was elevated and trained by power as in A5-13. C1-18 had two periscopes called primary and secondary 'one for the Captain and the other for the look-out man continuously sweeping the horizon'. One was fitted in the conning tower as in previous boats and a support bracket appears for the first time. The other was just aft of the conning tower. Both periscopes were raised by hand purchase but were power trained by ½hp motor. In previous boats the diameter of the periscope tube was 4in. throughout but in C1-18 the diameter of the main tube was 4in. and the upper end 3in. The conning tower periscope was 12ft 4in. long and the top of the periscope when raised was 7ft 11in. above the support bracket.

25. A statement has been seen to the effect that 'in C12-16 the external diameter of the periscope tube was Increased to 5⅜in to allow a stereoscopic optical arrangement to be introduced. This principle was found to be unsatisfactory and the periscope converted to the monocular type although the larger diameter tube was retained and became standard practice'. The diameter 5⅜in quoted is thought to be an error and should be 5⅝in as fitted in C19-38 and also in the E Class.

26. C12-16 were completed early in 1908 and the builders state that the periscopes were as in C1-11 except that they were 12ft 9¾in. long. The stereoscopic arrangements mentioned in Paragraph 25. may have been tried after the boats had been completed. In spite of the fact that the principle had been found to be unsatisfactory, one stereoscopic periscope only was fitted in C21-38 and probably in C19-20. It was manufactured by Howard Grubb and cost '£465 each, including erection in the boat, brackets and material for manipulating'. The periscope was 21ft long; the periscope bracket was fixed to the after side of the conning tower with the top of the bracket 3ft 6in above the bridge deck. In the raised position the headpiece of the periscope was about 9ft above the bracket. A deep recess was fitted in the battery tank so that the periscope could be lowered about 10ft to allow the top to be housed in the periscope bracket. This was the beginning of periscope wells. The periscope was elevated by hand purchase which was changed in C31-38 to electric control; no training gear was fitted.

27. D1 at first appears to have had an experimental outfit of periscopes; see Plate 9. The primary periscope in the bridge appears to have been of the ball joint type very similar to that used in the Holland boats, raised and lowered by leads from the capstan. The secondary periscope is shown aft between the main motors. These arrangements seem so fantastic that it is hard to believe they were ever fitted. But something did happen because the builder's records give no information other than they were hand elevated, whereas for other boats they give detailed Information. If ever fitted they were changed later.

28. D3-8 had two periscopes approximately 26ft 6in long with two large periscope standards which stood nearly 6ft above the bridge deck. The external diameter of the periscope main tube was 5⅞ in and of the 4ft top portion 3½in . When fully raised the top of the periscope was 9ft 11½in above the top of the brackets. Periscope wells were fitted so that the periscopes could be lowered sufficiently for the tops to be fully housed in the periscope brackets. The policy of periscope brackets and wells is by now fully established. The forward periscope was about 6in to starboard of the middle line to clear the drop keel release gear fitted on the centre line below. The arrangements in D2 were similar except for the position of the periscopes.

The method of elevating the periscopes varied within the class. Some had hand purchase and others 2hp motors. In D3 the same motor as for the steering gear was used. No arrangements were fitted for training the periscopes.

29. Prior to 1911, Sir Howard Grubb held the monopoly for periscopes for RN submarines. The periscopes were bad both as regards strength and vibration. Furthermore Vickers (who built for Grubb) apparently did not use non-magnetic steel tubes since they could not be obtained in this country. In 1911 representatives of DNC and Commodore (S) visited the works of Officino Galileo in Florence, Messrs Goertz in Berlin and Messrs Lacour-Berthiot in Paris. In all cases the periscopes shown were optically and mechanically better than the British types.

As a result of these visits orders were placed in 1912 for six German (Goertz) periscopes, and a further six were ordered later, and for one French (Lacour-Berthiot) periscope for trial.

Details of the Goertz periscopes are not known but comparative figures of the French and Grubb types were:

External diameter  5. 625 in 4. 646 in
Length from eyepiece to centre line of upper prism 21. 04ft 21. 32ft
Weight Less than 617lb 617lb
Cost £465 £480

The Lacour-Berthiot periscope was fitted in C34 for trial and proved very satisfactory especially in the small diameter of the top of the periscope of only 2⅝in. This was a good feature in all French periscopes.

What exactly happened to the Goertz periscopes is not known but neither the French nor the German periscopes appear to have been adopted. However some good came from this exercise and the Grubb periscopes were improved. In E1-6 the periscope tubes were made of brass and later boats had non-magnetic steel tubes.

Messrs Kelvin Bottomley and Baird manufactured Italian periscopes for S1 and presumably arranged to work the Galileo rights in this country. They later on got similar rights to work the Goertz patents.

30. As a matter of interest, relevant to this period Domville-Fife in his book published in 1910 states:

The C boats were fitted with two periscopes instead of one. The reason being that the range of vision of this instrument is barely 60° and thus, as we suppose to have been the case in the accident to A1. It is impossible for the officer in command to keep constantly in view a certain portion of the surface when the vessel is submerged. The two periscopes obviate this difficulty.

Vision when submerged is most difficult. The range of vision is small and in a rough sea it is impossible to see any distance ahead. Much has been said about the vibration of the periscope caused by the propelling machinery and the water friction on the periscope tube. This however is not the case in the latest boats.

It is not certain which were the 'latest' boats mentioned in this statement but it is probably C19 onwards. In the B Class with 9ft 6in periscopes the unsupported length when raised was about 6ft; corresponding figures were 12ft 4in and 8ft in C1-18 and 21ft and 9ft 6in C19-38. The D Class were not yet at sea. Although the length of periscope had increased the unsupported length had been kept to a reasonable figure by the arrangements inside the boat and the use of periscope brackets. A reduction in vibration might have been obtained from increase in strength of the periscope tubes in C19 onwards but it was probably optimistic to suggest that these later boats were free from vibration.

31. The E Class had two periscopes, one low power and the other high power about 23ft long, diameter of main tube 5⅝in reduced to 3⅝in for the top 4ft. As a result of war experience they were fitted with a sky-searcher for detecting aircraft. They were power elevated by electric motor although pneumatic elevation was tried in E4 and E5 and perhaps a few other boats of the class. In E1-11, and perhaps a few more, the periscopes were power trained using a ½hp motor. Thereafter no special training gear was fitted.

32. Other than for the periscopes themselves a pattern had now been set which was followed in principal through to the 1930's but for a few exceptions which are mentioned later. Two periscopes were usually sited, one forward and one aft of the conning tower with periscope brackets attached to the conning tower casting. As the periscope brackets increased in height they were structurally tried together at the top. Periscope wells were normal. Periscope training was by hand; elevation was by electric motor until telemotor hoists were introduced in the J Class. A great improvement was made in the telemotor system in this class which did not apply to other classes finishing at the same time e. g. the last of the E boats and the G Class all had electric elevation of periscopes. From the J Class and K Class telemotor elevation became standard practice.

The length and size of periscopes varied with the size of the vessel and the policy at the time. Further discussion on this point is given in Paragraph 35.

33. Points of interest in later classes are:

  • The K Class had one Grubb and one Kelvin type 30ft periscope, the longest yet fitted.
  • Similar periscopes as above were fitted in the L Class. A structural tie was fitted between the tops of the periscope brackets. A third Kelvin (night) periscope was sited between the two main periscopes which was about 13ft long, was hand operated and viewed from the conning tower. No bracket was fitted for this Kelvin periscope the upper bearing being in the structural tie between the two main periscope brackets.
  • In the M Class one of the main periscopes was used for range finding. An extra periscope for gun control was fitted to the director tower just abaft the 12-inch gun.
  • Although much smaller boats the R Class had 30ft periscopes with a travel of about 13ft. When housed the tops of the periscopes were below the level of the bridge side plating,
  • X1 had three periscopes one 7½in 30ft long, one 7½in 36ft long and one 8½in 42ft long.
  • The Oberon Class and Odin Class, Parthian Class and Rainbow Class had two 40ft periscopes, one 9½in and one 7½in . In Oxley and Otway both 40ft periscopes were 7½in.

34. The number and length of periscopes in the various classes are given in Appendix V together with the depth from the top of the highest periscope to the underside of keel. Most of the details given above for the periscopes in the Holland to E Class wer eobtained from the records of the builder (Vickers). Details for boats built by other yards may vary from those given.

35. As periscopes grew in length so did periscope standards and this brought to the fore two problems, that of silhouette and also the ability to dive in shallow water. It was well known that the longer the periscope the better was control at periscope depth. In the late 1920's means of passing through nets was also being tackled seriously.

The position was reached when the length of periscopes had to be decided on the following points:

  • (a) Height of the periscope standards and their effect on silhouette and in passing through nets.
  • (b) Overall depth to underside of keel with periscopes up for diving in shallow water.
  • (c) Submerged control.
  • (d) Submarine at periscope depth to be clear of small vessels such as destroyers passing over her.

Items (a) and (b) are in opposition to (c) and (d).

36. In the late 1920's invisibility was considered most important and this was undoubtedly based on experience during the 1914-18 war. There was a large school of submarine officers to whom minimum silhouette constituted one of the major items in submarine design to be obtained at the cost of anything else. At the same time silhouettes were growing with items such as the Captain's cabin in the bridge, bridge canopies, upper deck galleys, above water hydroplanes and above everything high periscope brackets. But the desire for longer periscopes usually won the day as for example in the Swordfish Class design in 1929. DNC proposed 30ft periscopes to keep down the height of the periscope standards and also incidentally to save weight which was most important in these vessels. He also stated that 34ft periscopes were the longest length practicable, RA (S) considered it was essential to have the maximum length possible and before the Controller would agree to a length of only 34ft he referred the question for confirmation that item 35(d) above was met. But there is no doubt that the long periscopes with high periscope standards fitted in the later vessels had great disadvantages in weight and silhouette, in diving in shallow water and in passing through nets.

Chapter 21: Rudder and Steering GearChapter 23: Pumping and Flooding Arrangements