IJN Submarine Floatplanes

In 1939, Japan essentially standardized its large submarine type with a vessel design displacing about 2,100 tons capable of cruising for 14,000 miles at 16 knots, or 24,000 miles at 10 knots, and diving to 330 feet. Three models were produced: a headquarters type emphasizing communications and command facilities, an attack type emphasizing torpedo armament, and a scouting type that added hangar space and a catapult for a small reconnaissance floatplane. Some 46 of these large submarines were constructed, as well as three others that brought together the facilities of all three types into the sen-toku type, a single monster hull displacing 3,530 tons standard.

Aichi M6A1 Seiran, portable strike monoplane torpedo-bomber
Caspar-Heinkel U-1, dismantable reconnaissance biplane
Watanabe E9W1 "Slim", portable reconnaissance biplane
Yokosuka E14Y1 "Glen", light reconnaissance monoplane
Yokosuka E6Y1-N, small reconnaissance biplane

List of submarine carriers
    Total = 42
    I-5 Type J1M scouting submarine: One built. (The First IJN submarine to carry a floatplane, completed 1 July 1932. No catapult was fitted, the I-5 aircraft was assembled on deck and lowered into the water for takeoff. Had two hangars).
    I-6 Type J2 scouting submarine: One built. (Carried one floatplane)
    I-7 and I-8 Type J3 scouting submarine: Two built. (Carried one floatplane, fitted with fixed catapult aft and twin hangars).
    I-9, I-10, I-11 Type A1 headquarters submarines: Three built. (Carried one floatplane, two more canceled 1942).
    I-12 Type A2 headquarters submarine: One built. (Carried one floatplane, hangar and catapult fitted forward).
    I-13, I-14 Type AM (A modified) aircraft carrying submarine: Two built. (Carried two floatplanes, catapult forward. Two not completed and three more cancelled).
    Type B1 scouting submarine; numbered I-15 through I-39: Twenty built. (Carried one floatplane, hangar and catapult fitted forward).
    Type B2 scouting submarine; numbered I-40 through I-45, Six built. (Carried one floatplane, hangar and catapult fitted forward. Numbers 702 through 709 cancelled).
    I-54, I-56, I-58 Type B3/B4 scouting submarine: Three built. (Carried one floatplane, hangar and catapult forward. 12 more cancelled) I-58 had aircraft and catapult replaced by Kaiten.
    I-400, I-401, I-402 Type Sentoku aircraft carrying submarine: Three built. (Carried three floatplanes, catapult forward. Were designed specifically to launch floatplane bombers against the Panama Canal. Two not completed, others cancelled).

TYPE J1M (1931): The I-5 was a version of the Type J1 enlarged to accommodate two tubular hangars for a dismantled seaplane and a launching catapult. The destroyer escort Wyman sank it east of Guam on 19 July 1944.

TYPE J3, I- 7 ( 1935): This class was an enlargement of the Type J2. They were fitted as squadron flagships. In 1943 one 13.2mm mount was replaced with a twin 25mm antiaircraft mount. The I-8 received a twin 5.50 mount in place of its single weapon in mid-1943 and was converted to a kaiten carrier in late 1944 by removing the 5.50 weapons, the hangar, and the catapult and replacing them with cradles for four human torpedoes. The destroyer Monaghan sank the I-7 near Kiska on 5 July 1943, and the destroyers Morrison and Stockton sank the I-8 near Okinawa on 31 March 1945.

TYPE J2 (1934): The I- 6 was similar to the I- 5 but fitted with a dual-purpose deck gun. The destroyer escort William C. Miller sank it off Saipan on 14 July 1944.

TYPE J3, I- 7 ( 1935): This class was an enlargement of the Type J2. They were fitted as squadron flagships. In 1943 one 13.2mm mount was replaced with a twin 25mm antiaircraft mount. The I-8 received a twin 5.50 mount in place of its single weapon in mid-1943 and was converted to a kaiten carrier in late 1944 by removing the 5.50 weapons, the hangar, and the catapult and replacing them with cradles for four human torpedoes. The destroyer Monaghan sank the I-7 near Kiska on 5 July 1943, and the destroyers Morrison and Stockton sank the I-8 near Okinawa on 31 March 1945.

TYPES B1 (1939), B2 (1942), AND B3 (1943), I- 30 ( 1940): The Type B submarines were longrange scouting boats equipped with a seaplane hangar and catapult. The Type B3 boats had less powerful diesel engines and were slower but had a greatly enhanced range. The I-36, the I-37, the I- 44, the I-56, and the I-58 were converted to kaiten carriers in late 1944, losing their deck guns, hangars, and catapults and receiving cradles for four to six human torpedoes. An additional 8 Type B2, 18 Type B3, and 18 Type B4 (enlarged Type B3) boats were canceled in 1943.

The I-23 failed to return from a patrol to Hawai’i in February 1942; the U.S. submarine Tautog torpedoed the I- 28 near Truk on 17 May; the I-30 was mined near Singapore on 13 October; the destroyer McCalla sank the I- 15 off San Cristobal on 2 November.

The destroyers Edwards and Farragut sank the I-31 off Kiska on 12 May 1943; the New Zealand trawler Tui sank the I- 17 near Noumea on 19 August; the destroyer Patterson sank the I- 25 in the New Hebrides on 3 September; U.S. aircraft sank the I-19 near Makin on 18 October; the submarine Taurus torpedoed the I-34 off Penang on 13 November; the destroyers Frazier and Meade sank the I- 35 off Tarawa on 23 November; the destroyer Radford sank the I-40 near Makin on 25 November; the destroyer Boyd sank the I- 39 in the same area the next day; aircraft from the escort carrier Chenango sank the I-21 in the Gilbert Islands on 29 November.

The British destroyers Paladin and Petard sank the I-27 near Addu Atoll on 12 February 1944; the submarine Aspro torpedoed the I- 43 east of Guam on 15 February; the U.S. submarine Tunny torpedoed the I- 42 near Anguar on 23 March; the destroyer escort Manlove and the submarine chaser PC-1135 sank the I-32 off Wotje the following day; the I-33 was lost in an accident near Iyo Nada on 13 June; the submarine Sawfish torpedoed the I- 29 in Balintang Channel on 26 July; the I-26 failed to return from a patrol off Leyte in October; the destroyer escort Richard M. Rowell sank the I- 54 in Surigao Strait on 26 October; the destroyer escort Whitehurst sank the I- 45 there on 29 October; the destroyer Nicholas sank the I-38 south of Yap on 12 November; the destroyer escort Lawrence C. Taylor sank the I-41 east of Samar on 18 November; the destroyer escorts Conklin and McCoy Reynolds sank the I- 37 off Leyte on 19 November.

The destroyers Collett, Heerman, Mc-Cord, Mertz, and Uhlmann sank the I-56 off Okinawa on 18 April 1945, and aircraft from the escort carrier Tulagi sank the I-44 there on 29 April. The I-36 and the I-58 were surrendered in August and scuttled.

TYPE A1 (1939): These boats were fitted as flagships for submarine squadrons with extra staff accommodations and more powerful communications equipment. Two additional boats were canceled in 1942. The destroyer Frazier sank the I-9 off Kiska on 11 June 1943; the I-11 failed to return from a patrol to the Ellis Islands in January 1944; the destroyer David W. Taylor and the destroyer escort Riddle sank the I-10 east of Saipan on 4 July.

TYPE A2 (1943): This boat received less powerful engines than the Type A1 class, sacrificing speed on the surface but greatly increasing its range. It failed to return from a patrol to the central Pacific in January 1945.

TYPE AM, I- 14 (1944): This class was a substantial expansion of the earlier Type A headquarters submarine design with two aircraft and a heavier antiaircraft battery. Only the I-13 and I-14 were completed; construction of the other boats was halted in March 1945. Three additional submarines were canceled in 1943. Aircraft from the escort carrier Anzio sank the I-13 near Truk on 16 July 1945, and the I- 14 was surrendered in August and scrapped.

TYPE STO (1944): This class was designed to launch aircraft for operations against cities of the U.S. mainland. These boats were the largest submarines built until after World War II. They had double pressure hulls over three-quarters of their length, placed one above the other forward and side by side over their midships section. They were commissioned with search radar and snorkel equipment. One additional unit was canceled in 1942 and 14 further boats in 1945. U.S. carrier aircraft sank the incomplete I- 404 at Kure on 28 July 1945. The three other boats were surrendered in August and used for trials by the U.S. Navy before they were scuttled in 1946.

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