During World War II, the Japanese began building submarines to carry bomber aircraft. The purpose was to bomb US cities because they believed that this would prevent their great adversary from attacking and consolidating in the Pacific Ocean.

But the Japanese did not have enough ships to do so, and as they thought, the construction of submarines would be the best option for their situation.

The inspiration came from the successful use of German submarines U-Boats. They were the largest submarines ever built. Length 122 meters and width 12. It was one of the most secret weapons of Japan.

They started making them in 1943 and were the first of their kind. They had a place to carry 3 special seaplanes that would bomb American territory. These aircraft would take off from the deck with a catapult running on compressed air. There was also a crane to pick up the planes that would land on the water. There were still five cannons on the deck and eight torpedo tubes inside. They were made to travel thousands of miles without refueling and were covered with a special paint to absorb sonar waves.

The goal was to build 18 units but by the time the first one was completed, the scales began to tilt in favor of the US. Eventually, by the end of the war, three had been built.

The end result was that no one had time to be sent on a mission to help Japan in the war.

For the time being it was a technological marvel that revolutionized the subsequent improvement of submarine construction.

[Source: http://www.businessinsider.com]