So were the "aircraft carrier submarines" I-400 with which Japan wanted to hit the US in World War II

During World War II some of the most extreme military projects in history emerged. Since the production of the United States’ first nuclear weapons to Nazi Germany’s plan to “fry” its enemies using a powerful space mirror. The Empire of Japan was not far behind and he built some submarines that, technically, were also aircraft carriers.

The emergence of this peculiar project had its origins in 1941, shortly after the military attack on Pearl Harbor. The Japanese wanted to take advantage of the surprise offensive against the US naval base to deal a heavy blow to the enemy mainland. The problem was that the targets were too far away for their planes to reach. collect World War II Database.

A new class of submarine is born, the I-400

Given this scenario, Admiral Isoroku Yamamoto, who had been in charge of organizing the offensive at Pearl Harbor and was the top leader of the Japanese Combined Fleet, had an idea: to build a series of submarines capable of carrying planes. could get close enough to the west coast of the United States, attack and return, all without the need to refuel.

It was not a crazy approach, but a serious project with which they thought they could get even more advantage in the war scenario of that time. Thus, the admiral formally presented his proposal at the Fleet Headquarters on January 13, 1942. It contemplated building eighteen submarines. The military commanders acted quickly and did not take long to give the green light to the project.

In a few months the general plans of the submarine were developed and in January 1943 the construction of the first ship began. The I-400, a new class of military vessel with a catapult aircraft launch system, was being born. Almost in parallel, the construction of another four more also began, the I-401 (April 1943), the I-402 (October 1943) and the I-403 (September 1943).

The project seemed on track, but things were changing. America’s military and industrial capacity was growing, and Japan was beginning to wear down. The Battle of Midway was a turning point for the Asian country. In that air-naval combat, the Imperial Japanese Navy lost several of its submarines and in this scenario of weakness it decided to reduce the number of I-400 submarines to just nine.

Characteristics of the I-400 class

At that time, the I-400 class submarines they were the biggest in the world, only surpassed later with the arrival of strategic nuclear submarines capable of launching ballistic missiles. The Japanese ships were 120 meters long and 12 meters wide. Each had four 1,680 kW (2,250 hp) engines and carried enough fuel to circle the world at least once. explains Combined Fleet.

These ships had a speed of 18.7 knots (34.6 km) on the surface and 6.5 knots (12.0 km) when submerged. Interestingly, the maximum depth of immersion was 100 meters, somewhat less than the total length of the submarine. This presented a problem when maneuvering in emergency scenarios. If the sub dived at too steep an angle it could put the crew at risk.

And now the most interesting. On the upper deck was the cylindrical hangar 31 meters long and 3.5 meters in diameter to accommodate a maximum of three aircraft. It was a completely airtight space that was sealed with a 51-millimeter-thick rubber gasket. Additionally, it had a collapsible crane with an electrically operated hoist that was capable of lifting approximately 4.5 tons. This raised the seaplanes and placed them inside the submarine.

But it wasn’t just a “mothership” that carried planes inside. She was also heavily armed. She had eight torpedoes in the bow. Above the hangar were three triple-mounted 25mm autocannons. On the bridge there was a 25 mm automatic cannon. On deck was also a 140mm long-range gun.

An aircraft specifically designed for the submarine

Transporting a fully functional, mission-ready aircraft inside a submarine was a major challenge. The aircraft at that time did not meet the requirements, so the design of a model specifically designed to fulfill those functions.

We are talking about the Aichi M6A Seiran, a two-seater seaplane equipped with a 1,410 hp Aichi AE1P Atsuta 30 engine built under license from the Daimler-Benz DB 601. The most interesting feature of the plane is that it folded so that it could enter the mother ship.

The war scenarios don’t give extra time, so there was no time for the plane’s engines to get up to temperature before their mission. However, the Japanese devised a technique to save time. Before each catapult launch, they injected hot oil into the aircraft, so it was ready to fly with a “cold start”.

At the level of armament, the Aichi M6A Seiran could carry a single 850 kg torpedo or its equivalent weight in bombs. In addition, he had a 13mm machine gun.

The precipitous end of the project

Finally, only three I-400 class submarines were built, between December 1944 and July 1945, but none managed to participate in a real battle scenario, although several attacks had been planned. In December 1945, the United States had carried out the atomic bombing of Hiroshima, followed by a similar attack on Nagasaki.

What followed was the surrender of the Empire of Japan and the control by the United States of these submarines and other ships of the Imperial Japanese Navy. Finally, the three that were finished plus those that were under construction were destroyed by the Americans to prevent the technology from falling into the hands of the Soviets, who had asked to inspect them.

Images | Wikimedia Commons

In Xataka | Ships sunk in World War II emerge from the sea in Japan: this is how nature has rescued these war shipwrecks