In our previous video, The Surprisingly Long and Determined Effort to Create a Literal Flying Tank, we looked at how designers in the 1930s and 40s devoted a considerable amount of time and effort trying to combine two of the 20th Century’s most revolutionary weapons of war: the tank and the aeroplane. But as ill-conceived and ultimately futile as these projects were, they were far from the strangest attempts to create a hybrid military vehicle. That dubious distinction instead belongs to an improbable series of efforts to mash together the two unlikeliest of vehicles: the aeroplane…and the submarine.

It will come as no surprise to regular viewers that the first nation to tinker with such a vehicular abomination was the Soviet Union. In 1937, while studying at the Dzerzhinsky Naval Engineers’ Academy in Saint Petersburg, Soviet engineer Boris Ushakov drafted a technical proposal for a vehicle which could operate both in the air and underwater. Featuring thick, stubby wings resembling a manta ray and a pair of floats for takeoff and landing, Ushakov’s flying submarine would be powered by three 800-horsepower gasoline engines on the surface and an electric motor underwater, giving it a maximum speed of 100 knots in the air and 3 knots submerged. Once the craft landed, the transition from aeroplane to to submarine would be accomplished by sealing off the engine compartments with retractable metal plates and flooding empty spaces in the wings and floats, causing the craft to submerge. The cockpit would also be flooded, forcing the crew to retreat into a watertight compartment complete with conning tower and periscope from which the submarine would be controlled. The craft’s armament was to be two 18-inch torpedoes mounted under the hull.

But what possible use could any Navy have for such an outlandish vehicle? As absurd as it might seem, Ushakov’s concept actually filled a number of roles that aircraft and submarines of the time could not. While fast, agile, and able to carry large weapons payloads, aircraft of the 1930s were far from stealthy, a fact which became increasingly relevant with the wide-scale adoption of radar. On the other hand, submarines, while stealthy, were also extremely slow underwater and largely blind, relying on periscopes and hydrophones to track and home in on their targets. Aircraft and submarines were also largely ill-suited to attacking enemy ships in harbour, which were typically defended by extensive antiaircraft batteries and antisubmarine obstacles like booms and nets. Throughout the 1930s and 1940s, there were numerous attempts to solve these tactical shortcomings, such as the development by several nations of midget submarines capable of infiltrating harbours and other protected spaces. This approach was pioneered by the Italian Navy, whose elite Decima Flottiglia MAS unit of combat frogmen used specially-designed human torpedoes nicknamed maiale or “pigs” to carry out a series of daring raids against Allied shipping in Alexandria, Malta, and Gibraltar. The maiale were copied by the British – who dubbed them “Chariots” – and, along with more conventional midget submarines known as X-Craft, used in a number of unsuccessful attempts to sink the German battleship Tirpitz at her anchorage in Norway. Japanese Type A Ko-hyoteki  midget submarines participated in the 1941 attack on Pearl Harbour and two 1942 attacks on Sydney Harbour and Diego Suarez Harbour in Madagascar, while various German midget submarines like the Neger, Seehund, and Biber carried out attacks on Allied shipping in the English Channel in the final years of the war. However, none of these vehicles proved as effective as their designers had hoped. For one thing, they had a limited range, requiring them to be carried close to their target, launched, and retrieved by a larger mother submarine. They were also slow, difficult to control, and despite their small size, easily spotted and engaged by enemy defensive forces. Consequently, the vast majority of midget submarine operations ended in the death or capture of their crews.

Another potential solution to the stealth-vs-speed conundrum was the submarine aircraft carrier. In the 1920s, a number of submarines were built to carry a small reconnaissance floatplane in a special watertight hangar behind the conning tower. Once the submarine had surfaced, the aircraft would be removed from its hangar, assembled, and launched using a steam catapult built into the deck. Upon completing its mission, the aircraft would land alongside the submarine and be hoisted aboard using a crane. While both the French Surcouf and British HMS M2 cruiser submarines possessed this capability, the most famous submarine aircraft carriers ever built were the Japanese I-400 class. The largest submarines ever fielded during WWII and the largest ever built until the 1960s, the I-400s were designed to carry and launch three folding Aichi M6A Seiran floatplanes, each capable of carrying 900 kilograms of bombs. The Japanese Navy planned to use these unusual weapons to attack the Panama Canal, San Diego, and Ulithi Atoll, but Japan surrendered before any of these plans could be carried out. The three completed I-400s were captured by the Americans, examined, and scuttled to prevent the Soviets from learning their technological secrets.

But as impressive as they were, the I-400s suffered from a fatal flaw. Launching and retrieving aircraft took up to 45 minutes and could only be done while the submarines were on the surface, making them highly vulnerable to detection and attack. Boris Ushakov’s flying submarine, on the other hand, neatly solved this problem. The craft could theoretically cover vast distances of ocean at high speeds, allowing it to track down and shadow an enemy fleet. It could then land, submerge, and use the cover of darkness to attack the fleet before stealthily slipping away. The craft was also well-suited to infiltrating harbours, able to fly over minefields, anti-submarine nets, and other defences before landing in the harbour basin, submerging, and attacking enemy shipping using torpedoes. Indeed, the Soviet Navy saw sufficient merit in Ushakov’s idea to submit his proposal to its Scientific Research Committee for evaluation. But while the concept made it through two rounds of official evaluations and revisions, it was ultimately rejected as too impractical, and Ushakov’s vehicular chimera never made it off the drawing board.

But the allure of the flying submarine never truly died, and the following decades would see numerous attempts to resurrect the concept. In 1961, American inventor Donald V. Reid of Ocean Township, New Jersey, cobbled together various discarded aircraft parts to create a working flying submarine, which he rather unimaginatively dubbed the Reid Flying Submarine or RFS-1. Though far smaller than Ushakov’s design at only 10 metres in length, Reid’s vehicle worked on exactly the same principle. Looking like something out of a contemporary James Bond movie, in the air, RFS-1 was powered by a 65-horsepower engine and propeller mounted on a tall pylon behind the cockpit, while underwater it was propelled by a 1-horsepower electric motor, diving being accomplished by flooding the craft’s fuselage and twin pontoons. The transition from flying to diving, however, was a less than elegant process, requiring the pilot to remove the propeller and seal off the engine pod using a rubberized cloth cover. The craft’s open cockpit also required the pilot to use Scuba gear to breathe while submerged. Nonetheless, on June 9, 1964, RFS-1 made the world’s first – and thus far only – full-cycle flying submarine flight over the Shrewsbury River, flying at 10 metres altitude before submerging and achieving a speed of 2 knots at a depth of 2 metres. While the craft’s immense weight limited it to making short, low-altitude hops, Reid proved that a flying submarine was a workable proposition, inspiring dozens of future efforts to perfect the concept.

In the same year as Reid’s historic flight, the Proceedings of the U.S. Naval Institute published a study by Naval hydrodynamics engineer Eugene Handler examining the feasibility of a flying submarine. As in Boris Ushakov’s original 1937 concept, such craft were envisioned for use against enemy shipping in harbour or in closed, heavily-defended waters like those of the Baltic, Black, or Caspian seas. As the Navy article states:

“Handler writes of a possible craft with an operating depth of 25 to 75 feet, a submerged speed of five to 10 knots for four to 10 hours, airspeed of 150 to 225 knots for two or three hours and a payload of 500 to 1,500 pounds. He says it is believed these characteristics can be attained within a vehicle weighing 12,000 to 15,000 pounds. A little flying sub might carry out its mission and take its crew back. It could, Handler says, fly from a favourable location to its destination at minimum altitude to avoid detection by radar. At the completion of its underwater mission it could travel as a submersible to a location best suited for takeoff, become airborne and return to base…. The Bureau of Naval Weapons has recently awarded a contract to the Convair and Electric Boat Divisions of General Dynamics for analytical and design studies of the essential components and operational aspects of such a vehicle.”

In the same article, Handler also acknowledges the various technical and bureaucratic obstacles which had long held back the development of a flying submarine, stating that:

“The development of a practical flying submarine prototype will be both complex and laborious, but the potential returns are substantial and valuable. Consequently the concept of such a vehicle merits careful engineering examination rather than the overly optimistic accolade of a few imaginative enthusiasts and the simultaneous cold shoulder denial of the hard headed realist.”

Inevitably, like every other flying submarine project, Handler’s concept also never made it off the drawing board. However, it may have directly inspired an iconic piece of pop culture. While developing the 1965 television series Voyage to the Bottom of the Sea, producer Irwin Allen hired researcher Elizabeth Emanuel to compile an archive of existing underwater technology on which to base the show’s vehicles and props. Among the material Emanuel uncovered in her research was the U.S. Navy’s flying submarine study, which is thought to have inspired the very similar stingray-shaped vehicle prominently featured in the show and which first introduced the concept of the flying submarine to the general public.

One of the fundamental flaws with the flying submarine concept is the need for a strong watertight compartment for the crew, which significantly increases the weight of the vehicle and makes it difficult to achieve flight. If the crew are eliminated altogether, however, then this particular engineering problem suddenly becomes a whole lot simpler. The first attempt to launch an unmanned aerial vehicle or UAV from a submarines was made in 1946, when a U.S.-built version of the WWII German V-1 cruise missile called the JB-2 Loon was test-launched from the deck of the USS Cusk. These experiments ultimately resulted in the development of the SM-N-8 Regulus, the U.S. Navy’s first submarine-launched nuclear missile. While a significant leap forward, the Regulus was a fundamentally flawed weapon. Carried in special water-tight compartments built into the submarine’s hull, the Regulus could only be extracted and launched one the submarine had surfaced. This made Regulus-equipped submarines extremely vulnerable to detection and attack, just like the Japanese I-400 submarines before them. This problem was eventually solved by the development of the Polaris and Trident ballistic missiles and the Tomahawk cruise missile, which could be launched while the submarine remained safely submerged.

In 1991, the Strategic Arms Reduction Treaty or START signed by the United States and the Soviet Union left the U.S. Navy wondering what to do with half of its ballistic missile submarines, whose nuclear payloads had been outlawed by the treaty. This resulted in a flurry of proposals for alternative non-nuclear weapons to occupy this considerable underwater real estate. Among these was Project Cormorant, first proposed in 2003 by DARPA, the Pentagon’s advanced research projects agency. Officially designated the Multi-Purpose Unmanned Aerial Vehicle or MPUAV, the Cormorant was a 6-metre-long jet-powered drone designed to be launched from a submarine missile tube. Pushed out of the launch tube by compressed air, the Cormorant would rise to the surface before being launched into the air by a pair of rocket boosters. The wings would then unfold, the jet engine inlet and outlet would open, and the vehicle would fly off on its reconnaissance mission, covering a distance of up to 800 kilometres. Upon completing its mission, the Cormorant would return and parachute into the sea, whereupon the launching submarine would deploy a Remotely Operated Vehicle or ROV to attach a cable to the drone, allowing it to be winched back into its launch tube. While hardly the exotic convertible vehicle of Boris Ushakov and Donald Reid’s imaginations, the Cormorant nonetheless solved the decades-long problem of combining the speed and maneuverability of an aircraft with the stealth of a submarine. Unfortunately, in 2008 the MPUAV project fell victim to budget cuts and, like all its predecessors, the Cormorant was never built.

Yet Ushakov’s dream still lives on, and shortly after the cancellation of Project Cormorant, the Naval Surface Warfare Center in Carderock, Maryland, released yet another proposal for a true flying submarine. 6 meters long with a 30-metre wingspan, the vehicle was designed to carry two crew and six Special Forces troops up to 1,200 kilometres by air or 20 kilometres underwater. While it is as yet unknown whether the Carderock flying submarine was ever built and tested, the fact that this absurd James Bond-esque vehicle continues to capture the imagination of Naval designers after nearly a century just goes to show that sometimes truth is sometimes stranger than fiction.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:

• That Time a WWII German U-Boat Sank as a Result of Flushing a Toilet
• This Day In History: A Yellow Submarine
• Briefcase of Armageddon (And How a U.S. Nuclear Barrage Would Be Carried Out)
• The Ridiculous Way British Sailors Were Ordered to Stop German U-boats During WWI