Chapter 15: Fleet Type Thames Class
1. By the end of 1922 only five K Class Fleet submarines of the seventeen vessels built remained in service and they had all been removed from the active list by early 1926. It is stated that the K Class were scrapped so early in life because they became too expensive a unit of the Fleet to maintain due to the wartime material used in their construction. They were also steam driven and this type of propulsion was not very popular with the submarine service. K26 was completed in June 1923 and taken out of service early in 1931, the year Thames was laid down.
2. In discussions between 1922-26 on the various types of submarines to be built, priority was given to the overseas patrol type and 'nothing useful could be done about Fleet submarines pending experience with K26 and X1 and further development of the IC engine.'
Between 1926-29 the functions and requirements for Fleet submarines were discussed at length. From the design aspect the controversial requirements were displacement and surface speed. The displacement was limited to not more than 1800 tons displacement (Geneva) the maximum agreed, but never fixed at the Geneva Conference. It was of course not known at the time that when the London Treaty ratified the findings of the conference, in October 1930, the maximum standard displacement allowed was 2000 tons. The speed asked for was 23-24 knots as designed with a certain 21 knots operational. This speed was not possible on the limited displacement allowed with the then state of diesel engine design.
3. At this time the requirements for the overseas patrol type submarines to follow the Rainbow Class were discussed. In 1928 RA(S) brought forward the question of speed in new construction - 'the operational speed of the Odin Class was really only about 15 knots (2 to 2½ knots less than the design speed) which was insufficient for submarines which, in an ocean wax, should be capable of operating with the Fleet'. He pressed for a general utility submarine with an operational speed of 18 to 19 knots. This found favour with C-in-C afloat.
4. It was eventually agreed that the type to accompany the Fleet and the faster overseas patrol type should be merged. As a result the Thames design was developed. Although not actually a Fleet type of submarine as originally envisaged but more of an improved patrol type, it was capable of accompanying the Fleet and could also be used for patrol or reconnaissance duties. It was decided that Fleet submarines of the Thames type should be built in future instead of the Odin type overseas patrol vessels.
5. The sketch design was submitted to the Board in June 1929. The main particulars were:
|Length overall||345 ft|
|Displacement standard||1760 tons|
|Speed surface||21 knots|
|Speed submerged||10 knots|
|Torpedo tubes, bow||Six 21-inch|
|Diving Depth||300 feet.|
Increase in weight during development of the design and building increased the final standard displacement to 1830 tons although 1805 tons was given officially.
6. Thames was in the 1929 Programme, was laid down in January 1931 and completed in September 1932. Severn in the 1931 Programme was not laid down until after Thames had completed. Clyde was in the 1932 Programme. All three vessels were built by Vickers-Armstrong's, at Barrow. Severn was generally similar to Thames but there were a few changes, which are mentioned below, where of importance. Clyde was a repeat of Severn.
If all had gone to plan and keeping within the limitations of the London Treaty, the eventual submarine force would have included twenty Thames Class submarines. However the policy changed circa 1933 and no more were ordered.
|Length overall||345ft 0in.||351ft 0in.|
|Beam maximum||28ft 3in.||28ft 0in.|
|Beam pressure hull||18ft 6In.||21ft 9in.|
|Displacement surface, tons||2165||2140|
|Displacement submerged, tons||2680||2530|
|Speed surface, knots||22.5||23.5|
|Speed submerged, knots||10.5||8+|
|Torpedo tubes, bow||Six 21-inch||Six 21-inch|
|Torpedo tubes, beam||Nil||Four 18-inch|
8. The Thames Class were double-hull boats except at the bottom where the pressure hull stepped down to the outer hull making the pressure hull of keyhole, section. To keep down weight so as to obtain the required speed the design diving depth was taken as 300 feet, as against 500 feet in Odin, with an operational depth of 200 feet. By doing this the pressure hull plating could be reduced to 25lb as against 35lb in Odin.
The oil fuel was carried in the external tanks of welded construction except for the connections to the pressure hull. There was also one internal oil fuel tank of 14 tons capacity.
The main differences in Severn from Thames were an increase in length of the motor room consequent on a change from the 330-volt battery grouping in Thames to a 220-volt grouping. The fitting of two escape chambers and main bulkheads to withstand a test pressure of 70lb/in2 instead of 35lb/in2, the deletion of the internal oil fuel tank and the strengthening of the hull structure in way of the main engine room.
9. In Thames the Loa was 345 ft 0 in, the Lbp 325 ft 0 in, breadth of the pressure hull 18 ft 6 in and of the outer hull 28 ft 3in and depth of the inner hull 18 ft 3 in. The figures for Severn were the same except that the breadth of the outer hull was 28 ft 2½ in.
The draughts in Thames were 15 ft 7½ in with main tanks empty, 15 ft 10½ in as inclined with about 40 tons of water remaining in the main tanks and 13 ft 6 in at the standard displacement of 1805 tons. Corresponding figures for Severn were 15ft 11 in with main tanks empty, 16 ft 3 in as inclined and 13 ft 9 in at the standard displacement of 1850 tons.
10. The legend surface displacement for Thames was 2155 tons and submerged displacement 2640 tons, which meant 485 tons of main ballast water. The surface displacement included 350 tons of liquids giving a standard displacement of 1805 tons, which was thereafter quoted for Thames.
As built, the displacements were submerged 2680 tons and surface with main tanks empty 2165 tons, which represent 515 tons of main ballast water. In this condition the reserve of buoyancy was 23.8%. In the inclined condition the surface displacement was 2205 tons, which means that 40 tons of water remained in the main tanks after being blown and the reserve of buoyancy was 21.5%.
The surface displacement of 2165 tons included 335 tons of liquids made up of oil fuel 224 tons, lubricating oil 38 tons, compensating and trimming water 32 tons and fresh and distilled water 41 tons. The standard displacement was actually now 1830 tons although 1805 tons was still quoted officially which was the accepted practice.
11. In Severn the displacements were submerged 2723 tons and surface with main tanks empty 2206 tons representing 517 tons of main ballast water. The reserve of buoyancy was 23.4%. As inclined the surface displacement was 2261 tons which means that 55 tons of water remained in the main tanks after blowing. The reserve of buoyancy was 20.4%. The standard displacement was fixed at 1850 tons in the legend stage.
The submerged displacement of Severn was 43 tons greater than that of Thames. The dimensions of these two vessels were identical, the capacity of the external main ballast and oil fuel tanks practically the same. The stability in Severn was greatly increased in all conditions from Thames. The only conclusion that can be reached from these facts is that buoyancy spaces of approximately 43 tons capacity were fitted in Severn probably in the superstructure. They could not have been buoyancy, tanks of the normal type, which could be flooded and blown because such tanks would have made little difference to the surface displacement and draught compared with Thames.
12. In the low buoyancy condition in Thames with Nos 2 and 6 Pt and Stbd main tanks blown the displacement was 2535 tons at 18 ft 10 in draught.
Corresponding figures in Severn were displacement 2582 tons at 19 ft 1 in draught.
14. In Thames the surface GM as inclined was 10.5 in, the submerged BG 5.0 in and low buoyancy GM with Nos 2 and 6 main tanks blown 3.9 in. These figures were lower than had been expected. The ballast keel weighed 80 tons.
At first Thames experienced heavy listing once on the surface from submerged due to water building up in the main tanks one side. The position of the flooding holes was modified to remedy this trouble. When surfacing beam on in a heavy sea, the vessel rolled heavily, this was accentuated by the large superstructure. It became the practice to surface head to sea in rough weather whenever possible.
Two changes in policy were approved about the time Thames completed both of which improved the stability figures given above. They were:
- (a) The 4.7-inch gun was replaced by a 4-inch gun, which had been adopted as the standard gun in submarines. This saved 6 tons of topweight.
- (b) The sg of oil fuel was changed from 0.871 to 0.842 with a decrease in weight of fuel of about 8 tons. These changes would increase the GM by about 1 in.
15. In Severn the surface GM as inclined was, 18.1 in submerged BG 11.2 in and low buoyancy GM 10.5 in. This was a considerable increase in stability from that in Thames as originally built. See Paragraph 11.
15.6 Speed and Endurance
16. The design surface speed was 21.75 knots at 10,000 bhp. On trials Thames obtained 22.57 knots at 9750 bhp and Severn 22.15 knots at 10,115 bhp. The full speed is taken as 22+ knots for the service speed of the class.
17. The legend surface endurance was 10,000 miles at 8 knots. Later figures given were 13,200 miles at 8 knots and 16,000 miles on one engine. Trial figures in Thames were 2400 miles at full speed and 16,100 miles at economical speed. Operational figures in 1938 were 3660 miles at 20 knots, 11,000 miles at 10 knots and 14,000 miles at 8 knots.
Corresponding operational figures in 1938 for Severn were 3430 miles at 20 knots, 10,100 miles at 10 knots and 13,100 miles at 8 knots.
18. The design-submerged speed was 10 knots at 2500 bhp; on trials Thames obtained 10.58 knots at 2585 bhp for one-hour duration.
19. The submerged endurance is given as 118 miles at 4 knots in Thames and 115 miles at 4 knots in Severn. The operational figures for Thames in 1938 were with auxiliary load (a) war load 170 amperes and (b) peace load 280 amperes:
|2 knots||4 knots||10 knots|
The auxiliary load in Severn was taken as war load 145 amperes and peace load 215 amperes which increased the endurances correspondingly e.g. to 1.5 hours at 10 knots.
20. The main ballast water was carried in the double-hull in external tanks port and starboard sides. The tanks were in the lower portion of the externals and flooding times were good, in fact in spite of the much larger superstructure the diving times were better than in the L Class. There was at first some trouble with the positions of the flooding holes, which were changed. The total capacity of the main tanks, including the bow buoyancy tanks, was of the order of 515 tons.
The oil fuel was in the external tanks above the main tanks. The tanks were constructed of the normal reasonably thin external tank plating and welded. After the problems experienced with the external fuel tanks in the Odin Class, Parthian Class and Rainbow Class it was gratifying that leaks from the external oil fuel tanks did not occur in Thames. However oil fuel did leak inboard in places through the pressure hull rivets. Thames as built had 224 tons of fuel of sg 0.871. The oil was later changed to sg 0.842 and the quantity fell to 216 tons. Severn had 202 tons.
15.8 Main Machinery
21. A vertical 4-stroke blast injection ten-cylinder diesel on each shaft developed 4000 bhp giving a total of 8000 bhp at 400 rev/min. They could be supercharged to give a total of 10,000 bhp. This applied to both vessels although slightly lower figures of 9750 and 9500 bhp have been given at times for Thames.
Two Ricardo sleeve-valve engines of 7½ in bore, 12½ in stroke, 400 bhp at 900 rev/min were fitted to drive two auxiliary generators which in turn could be used for charging the batteries or running the supercharger blower motors when main engines were on full power. The electrical characteristics of the auxiliary generators varied between Thames and Severn.
The machinery was of Admiralty design and fortunately the engine weight as built of 347 tons was 33 tons less than allowed in the legend weights. Without this saving Thames might have been in serious trouble with stability.
22. Tandem sets of main motors, one on each shaft, developed a total of 2500 bhp at 245 rev/min at 1¼ hour rating and 1320 bhp at 2-hour rating. They were guaranteed for a total of 3300 bhp at ½ hour rating. Slow speeds were obtained with the main motor armatures in series developing up to 50 bhp per shaft at 35 rev/min. An auxiliary drive was not fitted.
23. Three battery tanks had 112 cells each - a total of 336 cells. They were of large capacity Thames Chloride E1 68601 type with a discharge rate of 3910-ampere hours for 1 hour, 6860 ampere hours for 5 hours and 7830 ampere hours for 10 hours. The total weight, approximately 222 tons. The battery could be grouped in Thames to give 330 volts. This was changed in Severn to 220-volt grouping.
24. Six bow 21-inch torpedo tubes with twelve torpedoes. A 4.7-inch gun was at first fitted but was changed after completion to a 4-inch gun in accordance with the then submarine policy.