British Royal Navy T-class, the back-bone of Royal Navy`s WW-II submarines

The Royal Navy decided in 1930 to replace its rather unsatisfactory fleet of O, P & R class submarines as well as the ageing H-class. The requirement was for two classes of submarines, one to be a medium sized coastal type suitable for use in the North Sea and Mediterranean, this was the S-class and the other a long range ocean going type, this was the T-class. During design due note had to be taken of the limitations of the ‘London Naval Treaty’ requirements that allowed the Royal Navy only 16,500 tons of new submarine construction.

To make the class worthwhile the Royal Navy’s main requirement was for a submarine displacing about 1,000 tons, fairly heavily armed, and with patrol duration of at least 42 days. Also required was simplicity of construction, ease of handling, a greater torpedo armament than earlier classes and an increased speed of diving.

The design was finalized as a ocean going saddle tank type, the lead ship class prototype Triton entered service in 1937. After successful trials, and with slight dimensional modifications a further 21 boats, known as Group 1 and 2, were ordered between 1936 to 1939.

Once WW-II had started it was decided to order a further 40 units to be known as Group 3 boats, slightly modified to the Group 1 submarines. In total only 31 to 37 were built of the Group 3 boats. Many boats of the second group were modified for employment in the Far East; by transformation of several ballast tanks into fuel tanks, thereby increasing fuel load from 132 to 230 tons, and surface range from 8,000 to 11,000 miles at 10 knots. This increase in range, essential in a theatre where it took a week or more to get from base to operating area, together with increased stores capacity, enabled long patrols to be carried out.

The T-class operated successfully throughout WW-II, although 16 boats in total were lost, and remained in service- considerably modernized and rebuilt, into the 1970’s.

Specifications, T class, group 1:

Displacement (srf/sub tons):
Dimensions (L*B*D feet): 275`0*26`6*16`3
Propulsion: diesel-electric 2*1,250hp Vickers/Admiralty diesels , 2*725hp electric motors, 2 shaft
Speed (srf/sub knots):
Range (srf/sub n/miles@knots): 8,000@10/80@4
Diving depth (feet): 300
Complement: 8 officers 49 enlisted
Torpedo: 6*21" (533mm) internal bow torpedo tubes, 2*21" external bow torpedo tubs, 2*21" external beam/amidship torpedo tubes, total of 16 torpedoes 
Mines: 18 in lieu of torpedoes
Armament: 1*4" main deck gun, 3*0.303 machine guns


A total of 59 submarines were built in this class, 15 boats in group 1 entered service in during 1939-40, 7 boats in group 2 entered service in 1941, and some 37 boats of group 3 entered service during 1942-46.
Group 3 had a welded hull giving it a diving depth of 350 feet, they had en extra 20 mm Oerlikon cannon mounted on a platform aft of the periscope, an aft 21" torpedo tube and the two torpedo tubes amidship were empoisoned aft the conning tower angled to fire astern.

After the war some of the submarines from group 3 were modernized and extensively modified throughout its lifetime, including cutting of pressure hull and adding sections 12 to 20 feet long, exporting them to foreign countries serving into the 1970s-these were known as `T conversion` class.
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