HMS Thor - Design and Development

Design and Development

Design began in 1934 but was constrained by the 1930 London Naval Treaty restricting the total British submarine fleet to 52,700 tons, a maximum of 2,000 tons for any boat, and maximum armament of one 5.1 in (130 mm) gun. The "Repeat P"s, as the design was originally called, were intended to be large and powerful enough to operate against Japan in the absence of other British naval units. Britain was in a financial crisis and would have difficulty affording enough boats to meet their allowance.

It was expected from British work on ASDIC other nations would develop something similar. To that end a smaller vessel around 1,100 tons would avoid detection. In the face of expected enemy anti-submarine measures any attack would probably have to be made at long range without the aid of the periscope but on ASDIC. To counter the resultant inaccuracy a large salvo of at least eight torpedoes would be needed.

The eventual design had 8 bow torpedo tubes (two external), two external tubes amidships angled to fire forward, and a single 4-inch (100 mm)/50 caliber deck gun. Maximum diving depth was 300 ft (91 m). The design was finalised in 1935 and on June 24 the decision was made to drop the "Repeat P" designation and give all boats names starting with "T".

The ten-torpedo salvo was the largest ever fitted to an operational submarine. British operational planning at the time assumed international treaties would prevent unrestricted submarine warfare, and the main purpose of the submarine would be to attack enemy warships. In such a situation, a commander may only have had one chance to attack, so a large salvo was essential. T-class boats built later in the war changed the two amidships tubes to fire astern.

The lead boat, Triton, was ordered on 5 March 1936 and ran her first-of-class trials in December 1938. Fifty-three T-class submarines were built before and during the war in three distinct groups, although there were minor differences between boats within the same group. The second and third groups had the fuel capacity increased on many boats to 230 tons, giving a range of 11,000 nmi (20,000 km; 13,000 mi) at 10 kn (19 km/h; 12 mph).