The T-class combined internal and external tubes with a heavy forward battery. Early boats carried ten forward-firing tubes and sixteen torpedoes, while later boats such as HMS Thrasher carried eight forward-facing and three rearward-facing tubes, for eleven tubes and seventeen torpedoes in all. Only the six internal forward tubes could be reloaded. The revised arrangement kept a strong opening salvo and let a withdrawing submarine threaten pursuers from astern. Since Thrasher was laid down in November 1939, the change probably owed more to pre-war exercises, seakeeping concerns, and the handling of the bulbous bow than to later combat experience.
Chapter · 35:44-40:43
T-class tubes: forward concentration and escape fire
Thrasher's T-class layout combined a powerful forward attack with rear-facing tubes intended to deter pursuit after the strike.