A few World War II-era submarines had small waterproof hangars for floatplanes, but the concept itself largely failed to take off.

A “submarine aircraft carrier” sounds like something out of a James Bond film—an enormous platform that surfaces from the depths, before unveiling a flight deck of aircraft for villainous ends.

In reality, whenever “submarine aircraft carriers” have actually been tested, they have been far simpler in design. It is possible to fit a single disassembled aircraft into a submarine, then dive with the aircraft aboard—only to reassemble it and launch it from a catapult some time later. The plane in question helps to extend the submarine’s situational awareness, giving it a better sense of where its targets are and warning against potential threats such as enemy aircraft. A sufficiently large aircraft could even carry out bombings or other combat missions on the submarine’s behalf.

Several real-world navies have experimented with submarine-launched aircraft. The concept reached its high point during World War II, when Imperial Japan built a handful of enormous I-400 submarines, which could carry three attack aircraft across long distances. Japan even designed plans to use submarine-launched aircraft against the Panama Canal in an effort to disrupt one of America’s most strategically important routes. That attack never took place—but the submarines and the aircraft considered in its planning were very real. 

In the Interwar Years, Many Navies Toyed with Submarine Carriers

The attraction of combining an aircraft carrier with a submarine is obvious. The submarine is stealthy and secretive, and can approach an enemy’s coastline undetected—and then launch an aircraft, extending the weapons range of the submarine itself considerably. But the problems combining these two naval platforms presented are towering, as they both have almost contradictory requirements. 

Japan was hardly the first to experiment with aircraft-carrying submarines. Germany experimented with carrying a Friedrichshafen FF.29 floatplane aboard its U-12 U-boat in 1915. The United Kingdom soon attempted the same, with a Sopwith Schneider floatplane aboard the HMS E22. But those early “aircraft carriers” had a major disadvantage: their aircraft were carried openly on deck, where they were exposed to waves and weather—and where they prevented the submarine from diving, negating the submarine’s most important characteristic. 

During the 1920s, navies flirted with watertight aircraft hangars. Britain’s HMS M2 replaced its original 12-inch gun with a hangar housing a tiny Parnall Peto floatplane and carried a launch catapult on deck. The aircraft could scout ahead, land beside the M2, and then be craned aboard. France went even bigger with Surcouf, at the time the world’s largest submarine, complete with two 8-inch guns, 12 torpedo tubes—and one watertight aircraft hangar filled with one Besson MB-411 reconnaissance floatplane. The airplane was used to spot targets for Surcouf’s enormous guns, giving the submarine airborne reconnaissance capabilities. On the other side of the Atlantic, the United States experimented with the S-1, which carried a disassembled Martin MS-1 floatplane inside a cylindrical deck container. While all of these designs worked, none proved worth the effort in a technical sense.

But Imperial Japan took the concept the furthest, completing more than 40 aircraft-carrying submarines of various types. Early Japanese designs generally carried small reconnaissance aircraft that could be disassembled and stored inside watertight hangars. Aircraft such as the Yokosuka E14Y “Glen” gave submarines a reconnaissance radius far beyond what crews could see from the submarine’s conning towers.

Japan’s I-400 Carrier Submarines: Too Little, Too Late

Japan actually used these submarines operationally during World War II. An E14Y launched from I-7 surveyed Pearl Harbor and studied how much damage had been done after the December 1941 attack. More famously, I-25 launched an E14Y off Oregon on September 9, 1942. The airplane dropped two incendiary bombs near the coastal town of Brookings, near Oregon’s southern border with California, in an attempt to start a major forest fire. The damage was negligible, but the raid was significant as the war’s first bombing of the contiguous United States by an enemy aircraft.

Japan flirted with other plans for submarine-launched aircraft raids throughout World War II, but the expenses associated with the submarines and the competing priorities for the Imperial Japanese Navy doomed these efforts. The first of the eponymous class of large submarines, I-400, was built in 1943 and entered service in late 1944, but saw minimal action as the war turned sharply against Japan; only two other submarines in the class, I-401 and I-402, were completed before the end of the war. 

In early 1945, a series of devastating air attacks against mainland Japan led Japanese war planners to consider a range of operations to retaliate against the United States. In March 1945, after the catastrophic “Operation Meetinghouse” firebombing of Tokyo, the Japanese Navy’s 6th Fleet proposed an air raid on San Francisco in retaliation, but the General Staff rejected the plan. Three months later, the three submarines were also prepared for a strike on the Panama Canal, but the fall of Okinawa to American troops led Japanese war planners to redirect them against American forces on the Caroline Islands instead. They were en route to that mission in August 1945 when the Japanese government surrendered, aborting it.

Ultimately, the course of the war meant that the I-400 fleet could never really be used strategically, as was planned. The submarines’ lack of usefulness in the war meant that they were seen as a novelty, and were not pursued by any of the major navies during the Cold War. Still, decades later, the concept is intriguing. The technology of the 1940s made combining an aircraft carrier with a submarine cumbersome and, ultimately, not worth the effort. But the combination of stealth and strike reach that the concept offered is something that modern navies still pursue today. 

About the Author: Harrison Kass

Harrison Kass is a writer and attorney focused on national security, technology, and political culture. His work has appeared in Tablet, City Journal, The Hill, The Spectator, and The Cipher Brief. He holds a JD from the University of Oregon and a master’s in Global & Joint Program Studies from NYU. More at harrisonkass.com.

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