submarines were fitted with a 4-inch gun, a 20mm Oerlikon cannon on a platform aft of the periscopes and three 0.303-inch machine guns on removable mountings.
Additional orders in the 1941 and 1942 Programmes meant that a total of 31 modified T Class submarines entered service between 1942 and 1946, 21 of which were laid down at Vickers (although a number of these were ultimately completed at other yards). Of the 22 Group 1 submarines constructed, eight were built exclusively at Barrow.
Along with other British submarines, the T boats ordered in the 1941 and 1942 Programmes were fitted with surface and air search radar sets.
