A Class submarines were over 280 feet long and displaced 1385 tons (surfaced). Their two Admiralty diesels developed 4300hp, which gave a surface speed of 18.5 knots. The submerged speed was 8 knots, produced by two English Electric motors generating 1250hp. The radius of action of the A Class was 500 miles on the surface at 11 knots and up to 90 miles submerged at 3 knots.
The heavy armament consisted of six 21-inch bow tubes (two external) and four 21-inch stern tubes (two external) - with 20 torpedoes carried. The class were also fitted with one 4-inch gun forward of the conning tower, one 20mm Oerlikon cannon and three portable 0.303-inch machine-guns.
