Japanese I-400 series submarine aircraft carrier paved the way for naval innovations

December 14, 2024 by Lance Johnson

The Japanese I-400 series, including the I-401, were massive submarines equipped to carry and launch aircraft, far surpassing contemporary Allied naval technology during World War II.

These submarines, designed by Admiral Yamamoto, aimed to launch surprise attacks on U.S. cities from the sea, using sub-based aircraft capable of flying 600 miles.

The I-400 series faced delays and resource constraints, ultimately missing their intended impact on the outcome of World War II. However, they were considered for a final strike on the Panama Canal before Japan's surrender.

The submarines' design inspired modern naval innovations, including ballistic submarines and missile-carrying warships, and continues to influence strategic naval warfare tactics today.

The brief interaction between U.S. Lieutenant Commander Stephen L. Johnson and the I-401 submarine in 1945 highlights the technology that could have altered the course of the war and serves as a historical reminder of naval ingenuity.

Historic ingenuity of Japan’s I-400 submarine aircraft carrier

Imagine a submarine so massive, it can carry its own fleet of attack aircraft. This is not the stuff of science fiction but a real-life marvel from World War II, which continues to inspire modern naval warfare strategies. The Japanese I-400 series, including the I-401, were nothing short of revolutionary, and their story is one that could potentially rewrite history.

In September 1945, Lieutenant Commander Stephen L. Johnson, a 29-year-old up-and-comer, had a rather unexpected encounter with the I-401, one of the I-400 series submarines off the coast of Japan. As the Segundo approached the massive vessel, Johnson's crew realized they were looking at technology far more advanced than anything seen by the Allies during the war. The I-401, with its towering hangar and impressive armaments, was a sight to behold, extending nearly a football field in length and displacing 5,233 tons — three times that of Johnson's Segundo.

The I-400 series submarines were designed to be a strategic game changer, the brainchild of Admiral Isoroku Yamamoto, who sought to exploit American vulnerabilities through a series of surprise attacks. The plan was bold and ambitious: attack U.S. cities with sub-based aircraft, aiming to cause widespread devastation and sow chaos. Each I-400 class submarine could carry three state-of-the-art Aichi M6A1 Seiran planes, capable of launching even in extreme conditions, with a range of 600 miles.

Threats in the Panama Canal led to I-400 capture by the US Navy

Curiously, the I-400s faced their own set of challenges. Despite the initial zeal, the subs encountered numerous issues with production delays, resource scarcity, and the growing threat of Allied forces. By the time the I-400s were ready, the war's course had drastically shifted. Nevertheless, the I-400s were still considered a viable option for one final, devastating strike: an attack on the Panama Canal.

However, fate intervened, and the I-400s found themselves en route to surrender instead of execution. Commander Tatsunosuke Ariizumi, the architect of the I-400s, could not bear the dishonor and took his own life aboard the I-401. As the submarines surrendered to the U.S. Navy, their innovative design caught the attention of American naval strategists. Around the same time, the U.S. Navy began using planes that could be encapsulated in water-proof tubes so it could be carried on the submarine and be deployed at sea.

Today, the legacy of the I-400 series still echoes. Their advanced technology, particularly in underwater aircraft carriers and their strategic deployment capabilities, foreshadowed modern naval innovations like ballistic submarines and missile-carrying warships. The I-400s, though never fully realized in their original capacity, laid the groundwork for future strategic dominance at sea.

As military's continue to explore and innovate in naval warfare, the I-400 series serves as a remarkable reminder of the ingenuity that can shape the course of history. From a fleeting glimpse at the top-secret technology during World War II to its enduring impact on modern-day military tactics, the story of the I-400s continues to inspire.