Type J3

(Imperial War Museum photo, scanned from Polmar & Carpenter's "Submarines of the Imperial Japanese Navy")

These were the largest submarines completed by Japan before the war, and were intended as squadron flagships.  Their design was based on the KD (Kai Dai) type rather than the preceding J1 and J2 types.

Both patrolled off Hawaii at the start of the war, and the aircraft from I-7 performed a valuable reconnaissance mission over Pearl Harbor on 17 December 1941 (some sources say this occurred on 16 December).  I-8 received a twin 14cm mount forward in 1943, just before making a voyage to German-occupied France.  I-7 was lost in the Aleutians after being damaged by destroyer USS Monaghan on 22 June 1943 and again by patrol aircraft on 5 July.  I-8 was converted to carry Kaiten in late 1944, and was lost to destroyers USS Morrison and USS Stockton off Okinawa 31 March 1945. 

Units2 (None survived)
ShipsI-7, I-8
Year(s) Completed 1937-1938
Displacement2,525 tons / 3,583 tons
Dimensions358.5 ft x 29.8 ft x 17.3 ft
Machinery 2 diesels: 11,200 hp

electric motors: 2,800 hp

Speed23 knots / 8 knots
Range14,000 nm @ 16 knots
Armament 6x533mm TT fwd + 1x14cm/50 cal. (21 Torpedoes) + 1 seaplane.
Max. Depth100 m (330 feet)
Crew100 officers and men