Throughout World War 2 (1939-1945), the attack aircraft and attack submarine both played a critical role in the road to total and complete victory over the Axis powers for the Allies. Both fields were mastered by the United States where its airborne attackers helped subdue Italy and Germany across Europe while its submarine force thwarted Japanese efforts in the Pacific Theater. With the end of the war in 1945, United States Navy (USN) authorities began to entertain the idea of a "Submersible Seaplane" amidst a backdrop of ever-evolving technologies and the growing threat of the Soviet Union in the East. As its name implies, the submersible seaplane would have an inherent ability to cruise above the water line and dive into the Deep Blue to neutralize enemy surface vessels - namely Soviet shipping - combining the proven traits of both airborne attack platform and hunting submarine in one complete package.
The concept was considered as early as 1934 by Soviet engineer Boris Petrovich Ushakov who penciled out plans for a three-engined floatplane with attack submarine capabilities. The idea was presented to authorities in 1936 but not followed up on.
American studies flowed into the 1950s when, by 1955, turbojet and submarine technologies had matured to useful levels. The turbojet made its operational debut in the Second World War with a few shining examples before the end and much was garnered by the Americans and Soviets in regards to captured German U-boat technology at war's end. An early submersible seaplane offering was drawn up by the All American Engineering Company but this unconventional idea fell to naught for the time being - though USN interest in the subject continued into the 1960s.
The USN laid out its formal plans for an undersea seaplane attacker capable of Sea State 2 waters (smooth waves no more than 1.8 feet) able reaching cruise speeds of up to 225 miles-per-hour through the air with an operating altitude of about 2,500 feet. When fully sealed and submerged for the anti-ship role, the craft would be able to make headway at up to 10 knots down to a depth of 75 feet with a range out to 50 nautical miles max (or up to 10 hours underwater).
The primary armament of such a craft was in releasing torpedoes against enemy ships or dispensing naval mines to cut off key areas such as ports/harbors in the event of war. Beyond this, there was the possibility that the craft could also carry and release/recover special operatives conducting their clandestine operations - going where no traditional submarine in the USN inventory could go.
In 1962, North American Aviation engineer Donald Reid built his two-man (tandem seating) "Reid Flying Submarine", designated the "RFS-1", submersible floatplane as a private venture utilizing discarded aircraft parts and components. While able to display the traits needed, the USN was not sold on the idea and thus the project ended - the primary failing of the RFS-1 being its weight, limiting the craft to short "hops" about the water.
By this time, the concept of an undersea attacker was seen as more or less a feasible to USN authorities and defense industry personnel, leading to the concern of CONVAIR being handed a development contract in 1964 for such a solution. The company had already completed (and tested) the unique F2Y "Sea Dart" ski-equipped, twin-turbojet supersonic seaplane fighter from 1953 until 1957 for the service and five of these prototypes were built. While able to exceed the speed of sound as a seaplane (an impressive feat all its own), the project was ended due to the loss of an aircraft and its test pilot in November 1954 - this while overall results of the program were judged as poor for the intended role.
The company responded with a relatively large, two-man / three-engined design built with a ventrally-positioned, retracting ski component with wingtip supports for stabilizing on the water. The aircraft was given a boat-like hull for on-water operations and could be fully-sealed for submarine work. The cockpit section was stepped and given a small section of canopy for vision and housed two operating crew. The mainplanes were shoulder-mounted with sweepback noted along the leading edges only. The tail unit comprised split horizontal planes and twin vertical tailplanes.
Propulsion was decided on through a pair of turbojet engines for general take-off duties and a single turbofan engine to handle the cruising aspects of the craft when in flight. The aircraft could land under its own power on the surface of the water in the traditional way a flying boat or seaplane would. The take-off jets would provide enough power to raise the fuselage from the surface of the water to which the ventrally-mounted ski component would come into play for skimming. Fuel would be held in a forward and aft fuel store.
Undersea work would require some preparation on the part of the crew to ready the craft. This included sealing the air-breathing jet engines from the corrosive effects of salty sea water, cooling hot components, and reworking the buoyancy of the air frame through fuel / seawater balancing. A primary ballast tank would be backed by an auxiliary ballast tank buried in the bowels of the fuselage. To keep the vessel as streamlined as possible, the wing mainplane members would either fold over or sweep back for a smaller frontal footprint. Propulsion would have to be satisfied by an electric engine driving a propeller at the rear of the fuselage - a battery pack carried to supply the needed power.
The primary danger in all this was to the pilots who were to sit in a pressurized cockpit section - because of the hybrid nature of the aircraft, the section would be made jettisonable and floated by parachute when in flight or floated to the surface when submerged.
With all this in mind, the project persisted to the point that water and wind tunnel work was underway heading into the mid-1960s. However, the program was criticized and ultimately derailed by some in the Senate which saw no value in the novel project to USN capabilities and thus the program was ended in 1965.
With the cancellation of the Submersible Seaplane, the concept fell to the pages of history.
(OPERATORS list includes past, present, and future operators when applicable)
✓Ground Attack (Bombing, Strafing)
Ability to conduct aerial bombing of ground targets by way of (but not limited to) guns, bombs, missiles, rockets, and the like.
Equipped to search, track, and engage enemy surface elements through visual acquisition, radar support, and onboard weaponry.
✓Maritime / Navy
Land-based or shipborne capability for operating over-water in various maritime-related roles while supported by allied naval surface elements.
✓X-Plane (Developmental, Prototype, Technology Demonstrator)
Aircraft developed for the role of prototyping, technology demonstration, or research / data collection.
Serving Special Forces / Special Operations elements and missions.
42.0 ft (12.80 m)
30.0 ft (9.15 m)
12.0 ft (3.66 m)
20,944 lb (9,500 kg)
29,983 lb (13,600 kg)
+9,039 lb (+4,100 kg)
(Showcased structural values pertain to the base CONVAIR Submersible Seaplane production variant)
PROPOSED: 2 x Turbojet engines with 1 x Turbofan engine for aerial travel; 1 x Electrically-driven propeller for undersea propulsion.
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