fitted with a 20mm Oerlikon cannon, mounted on a platform aft of the periscopes, which replaced or supplemented three portable 0.303-inch machine-guns. 18 vessels, built towards the end of the war and intended to operate in the Far East, had their standard 3-inch gun replaced by a 4-inch gun, mounted inside a low breastwork, forward of the conning tower. In addition, the boats fitted with the 4-inch gun had their stern torpedo tube removed resulting from weight considerations.
To extend their radius of action, submarines operating in the Far East during the war had some of their main ballast tanks converted to oil fuel tanks, increasing the fuel load from 72 tons to a maximum of 98 tons. All boats stationed in this theatre proceeded on patrol carrying as much additional stores as possible - particularly food and ammunition - stowed in all
