Type A1 submarine

The Type A1 submarine (巡潜甲型潜水艦), also called I-9-class submarine (伊九型潜水艦) were a trio of aircraft-carrying cruiser submarines built for the Imperial Japanese Navy (IJN) during the 1930s. All three participated in the Pacific War and were lost.

Design and description
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. They displaced 2919 LT surfaced and 4129 LT submerged. The submarines were 113.7 m long, had a beam of 9.5 m and a draft of 5.3 m. They had a diving depth of 100 m.

For surface running, the boats were powered by two 6200 bhp diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 1200 hp electric motor. They could reach 19 kn on the surface and 8.25 kn underwater. On the surface, the A1s had a range of 16000 nmi at 16 kn; submerged, they had a range of 90 nmi at 3 kn.

The boats were armed with six internal bow 53.3 cm torpedo tubes and carried a total of 18 torpedoes. They were also armed with a single 40-caliber 140 mm deck gun and two twin 25 mm Type 96 anti-aircraft guns.

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.

Boats
Two more boats were ordered under the 1942 Naval Program, but were later cancelled.
 * JAPANESE SUBMARINE I-9 was sunk by destroyer USS Frazier in the Aleutians on 11 June 1943.
 * JAPANESE SUBMARINE I-10 was sunk by destroyer USS David W. Taylor and destroyer escort USS Riddle east of Saipan on 4 July 1944.
 * JAPANESE SUBMARINE I-11 disappeared south of Funafuti after 11 January 1944. The I-11 probably struck a mine laid by USS Terror.