Submarine aircraft carrier
Submarine aircraft carriers are submarines equipped with airplanes for observation or attack missions. These submarines became the biggest of the World War II, although they operational significance remained rather small. The most famous of them are the Japanese submarine I-400 and the French submarine Surcouf, although a few related attempts were made by a few other navies as well.
The Surcouf
Main article: French submarine Surcouf
During the first years of World War II, Surcouf was a French submarine ordered to be built in December 1927, launched 18 October 1929, and commissioned May 1934. At the beginning of World War II, Surcouf was the largest submarine in the world. Her short wartime career is laced with controversy and conspiracy theories.
Surcouf was designed as an "underwater cruiser," intended to seek and engage in surface combat. For the first part of that mission, it carried an observation float plane in a hangar built into the after part of the conning tower; for the second part, it was armed with not only ten torpedo tubes but also a twin eight-inch gun turret forward of the conning tower. The guns were fed from a magazine holding 600 rounds and controlled by a director with a 40-foot rangefinder, mounted high enough to view a seven-mile horizon. In theory, the observation plane could direct fire out to the guns' fifteen-mile maximum range. Antiaircraft cannon and machineguns were mounted on the top of the hangar.
I-400
Main article: I-400 class submarine
Although the U.S. Navy meant to keep it a secret forever, the Japanese were considerably ahead of the Allies in submarine development and underwater weapons. Recently, the result of a search in October last year for the Japanese Ghost Fleet, as it has been dubbed, was in the news with the discovery of the I-400 class of Japanese submarines, the largest in the world until the 1960s when the nuclear fleets were built.
During the Second World War, the Japanese had 30 different classes of submarines — from the one-man suicide torpedoes to the giant I-400 class of aircraft carriers. One class was the large attack submarine, the most famous of which was the I-58 which sank the U.S. heavy cruiser USS Indianapolis on its return voyage after delivering the Little Boy atomic bomb to the island of Tinian (the story of the loss of the USS Indianapolis and the attempted cover-up by the Navy and crucifixion of its commander, Captain McVay, is a fairly well-known story.) As the war turned against the Japanese and their fleet no longer had free reign over the Pacific, the Commander-in-Chief of the Japanese Combined Fleet, Admiral Isoroku Yamamoto, devised a daring plan to attack the cities of New York, Washington D.C., and other large American cities as well as to destroy the Panama Canal.
One of Yamamoto’s plans was the sen toku (secret submarine), able to carry three sei ran aircraft, each carrying an 800 kilogram (1,764 pound) bomb 650 miles at 360 miles per hour. Its name was combination of sei (clear sky) and ran (storm), literally “storm out of a clear sky,” because the Americans would not know they were coming. Three of the sen toku were built, the I-400, I-401, and I-402. Each had four 3,000 horsepower (2.2 MW) engines and fuel enough to go around the world one-and-a-half times, more than enough to reach the United States from either direction. It displaced 6,500 tons and was over 400 feet long, three times the size of ordinary submarines. It had a figure-eight hull shape for additional strength to handle the on-deck hangar for housing the three sei ran aircraft. In addition, it had four antiaircraft guns and a large deck cannon as well as eight torpedo tubes from which they could fire the Long Lance, the best and most deadly torpedo in the world.
The existence of the sei ran class of aircraft was unknown to Allied intelligence. The wings of the sei ran folded back, the horizontal stabilizers folded down, and the top of the vertical stabilizer folded over so the overall forward profile of the aircraft was within the diameter of its propellor. When prepared for flight, they had a wing span of 40 feet and a length of 38 feet. A crew of four could prepare and get all three airborne in 45 minutes. The planes were launched from a 120-foot catapult on the deck of the giant submarine. A restored sei ran airplane is on exhibit in the National Air & Space Museum in the Smithsonian Institute. Only one was ever recovered and it had been ravaged by weather and souvenir collectors, but the restoration team was able to reconstruct it accurately.
In the opening days of 1945, preparations were underway to attack the Panama Canal. The strategy was to cut the supply lines and access to the Pacific by U.S. ships. The plan was to sail westward through the Indian Ocean, around the southern tip of Africa, and attack the canal’s Gatun Locks from the east, a direction from which the Americans would not expect and were little prepared to defend. The flights would, of course, be one-way trips. None of the pilots expected to survive the attack, a tactic called tokko. Each pilot was presented with a tokko short sword, symbolic of the ultimate sacrifice.
Before the attack could commence from the Japanese naval base at Maizuru, word reached Japan that the Allies were preparing for an assault on the home islands. The mission was changed to attack the Allied naval base on Ulithi where the invasion was being assembled. Before that could take place, the Emperor announced the surrender of Japan. On August 22, 1945, the crews of the submarines were ordered to destroy all their weapons. The torpedoes were fired without arming and the sei ran aircraft were launched without unfolding the wings and stabilizers. When the I-401 surrendered to an American destroyer, the U.S. crew was astounded at its size. The commander of the air fleet, General Arizumi, had to atone for the surrender of the submarines with his blood. He requested that his body be wrapped in the Japanes flag and buried at sea. He then shot himself.
The U.S. Navy boarded and recovered 24 submarines including the I-58 and the sen toku, taking them to Sasebo Bay to study them. While there, they received a message that the Soviets were sending an inspection team to examine the submarines. To keep the technology out of the hands of the Soviets, Operation Road’s End was instituted. Taken to a position designated as Point Deep Six, about 40 miles west from Nagasaki and off the island of Goto Retta, the submarines were packed with charges of C-2 explosive and destroyed. The I-58 met the same ultimate fate of its target, the USS Indianapolis, the previous summer, and sank in 12 minutes. The I-402 was the last of the 24 submarines to be disposed of. In all, it took only three hours to scuttle all 24 of the Japanese submarines.
Some Japanese like to believe that the sen toku inspired the building of the large modern nuclear submarines and that the launching of aircraft from a submarine lead to the idea of launching ballistic missiles. This can be disputed since the largest submarines ever, the Russian Typhoon class, was built in ignorance of the sen toku. As soon as during the Second World War, US submarines had fired rockets from deck-mounted launchers against the Japanese mainland (the Japanese thought they were bombs from high-flying night bombers). Incidentally, the hulls of modern nuclear submarines do not feature the figure-eight shape of the sen toku, but were based on the shape of the German Walther boats that were developed toward the end of the war (The Germans themselves based their design on the shape of dolphins).