The submarines of the A1 type were versions of the preceding J3 class with superior range, improved aircraft installation.

Unlike the earlier boats, they were equipped with extensive communication facilities to allow them to serve as squadron flagships.

[1] For surface running, the boats were powered by two 6,200-brake-horsepower (4,623 kW) diesel engines, each driving one propeller shaft.

[3] Unlike the J3 class, the aircraft hangar was integrated into the conning tower and faces forward; the positions of the deck gun and the catapult were exchanged so the aircraft could use the forward motion of the ship to supplement the speed imparted by the catapult.

The hangar could be accessed from inside the pressure hull and the floatplane was stowed with its wings folded.