The first T Class submarines were 275 feet long and displaced 1327 tons surfaced. Their 'surface' armament included one 4-inch gun and three 0.303-inch machine guns, which were later replaced by, or supplemented by, one 20mm Oerlikon cannon. They were the last Royal Navy submarines designed for overseas patrol to have insufficient range for the Pacific.
One of the most distinguishing features of the Group 1 T boats was their high number of torpedo tubes: six bow tubes, which were reloadable from inside the pressure hull; two external bow tubes, contained in a bulbous bow casing; and two external tubes situated amidships, and so arranged as to fire ahead. This gave the class the phenomenal bow salvo of ten torpedo tubes which, the Royal Navy believed, would compensate for the inevitable errors that accompanied long-range attacks. As an alternative to
