I-400 Class Submarine Aircraft Carrier
The I-400-class submarine Imperial Japanese Navy (IJN) submarines were the largest submarines of World War II and remained the largest ever built until the construction of nuclear ballistic missile submarines in the 1960s. They were submarine aircraft carriers able to carry three Aichi M6A Seiran aircraft underwater to their destinations. They were designed to surface, launch their planes, then quickly dive again before they were discovered. They also carried torpedoes for close-range combat.
The I-400 class was designed with the range to travel anywhere in the world and return. A fleet of 18 boats was planned in 1942, and work started on the first in January 1943 at the Kure, Hiroshima arsenal. Within a year the plan was scaled back to five, of which only three (I-400 at Kure, and I-401 and I-402 at Sasebo) were completed. None were used operationally. I-400 and I-401 were evaluated by the US Navy in Hawaii and then sunk in deep water.
Photographs of scale models of the I-400 can be found here.
i-400 Class Photographs
Officers of submarine I-400, circa late Aug 1945 ww2dbase 
Japanese Crew on deck ready to leave the Japanese Submarine I-400 
I-400 with Japanese crew aboard after the Surrender in 1945 
I-400 Men pass cargo down the line 
Japanese crew mustered on deck after surrender. Note US sailors with guns 
Outermost sub, is the I-14 She carried two aircraft the two inner side boats are I-400 Class 
USS Euryale (AS-22)Sasebo, Japan, in November 1945. She has three large Japanese submarines alongside. They are (from inboard to outboard) I-401, I-14 and I-400 
Two I-400-class submarines and I-14 (right) 
I-401 and I-14 alongside of USS Proteus (far left), Yokosuka, Japan, 29 Aug 1945 
I-400 and another aircraft carrying submarine, alongside the USS Proteus at Yokosuka 
I-401 alongside of USS Proteus, Yokosuka, Japan, 29 Aug 1945 
I-400 Class Submarine 
I-401 
I 400 at Pearl Harbor 
2 captured I-400 class submarines and I-14 in Tokyo Bay, 1945 
I-400 Class Submarine with numerous other subs and ships 
At right are the ex-Japanese submarines I-14, I-401, and I-400 
Ex-Japanese subs I-14, I-401, and I-400 are in lower left. At right centre is USS Bowditch 27 February 1946 
I-400 class submarine sinking after being used as target
External Detail
I-400 Class after 5.5″ deck gun 
I-400 Class 25mm Guns on Deck
Hanger Detail
I-400, or I-401 Interior of the aircraft hangar, showing tracks for rolling planes out 
I-400 Inside of Hangar 
Hangar Watertight Door I-400 Class Submarine
Internal Detail
Main Control Room on the I-400 
Main Control Room on the I-400 
Main Control Room on the I-400 
I-400 inside Manoeuvring Room 
I-400 Main Starboard Engines 
Port Engine room I-400 
I-400 Man stands with Radar Gear 
Officer’s Quarters Amidship Port I-400 
I-400 Class Forward Upper Torpedo Room 
I-400 Class Crew’s Living Quarters aft
Aichi M6A Seiran
Aichi M6A Seiran 
Aichi M6A Seiran
