Submarine aircraft carrier

HMS M2 launching her Parnall Peto seaplane.

Submarine aircraft carriers are submarines equipped with fixed-wing aircraft for observation or attack missions. These submarines saw their most extensive use during World War II, although their operational significance remained rather small. The most famous of them were the Japanese I-400 class submarine and the French submarine Surcouf, although a few similar craft were built by other nations' navies as well.

The submarine aircraft carriers which were actually built, with the exception of the I-400 and AM classes, all used their aircraft in supporting roles, usually for reconnaissance. This is in contrast to the typical surface aircraft carrier, whose main function is serving as a base for combat aircraft.

Early history (World War I)

SM U-12 with a seaplane on deck

Germany was the first nation to experiment with submarine aircraft carriers, inspired by the Imperial German Naval Air Service commander Oberleutnant zur See Lothar von Arnauld de la Perière. He commanded a unit of two reconnaissance seaplanes (Friedrichshafen FF.29s) in Zeebrugge which had been recently occupied by the Imperial German Army in the early months of World War I. One of the first U-Boats to arrive at the Zeebrugge base was Kapitänleutnant Walther Forstmann's SM U-12, which was to play the role of submarine aircraft carrier.

Forstmann ordered the modification of the unarmed FF-29 seaplanes so they could carry 26 ¹⁄₂ pounds (12.0 kg) bombs. This unit made history when on 25 December 1914, one of its newly modified aircraft flew across the English Channel and up the River Thames, dropping its bombs on the outskirts of London where they did little damage. Although chased for a time by three British interceptors, it returned to base safely. On this first ever bombing mission it became apparent that the aircraft suffered more from fuel problems and lack of range than from British defences.

Later encouraged by this success, Arnauld and Forstmann theorized that they could effectively increase the range of their seaplanes by taking the aircraft to the sea on the deck of submarine and placing it in a takeoff position, then launching the planes after the sub partially submerged, allowing the plane to float off. On 15 January 1915, U-12 left their Zeebrugge base transporting one bomb-armed FF-29 on its deck. The submarine left the harbor, seemingly dwarfed by the 53 ft 2 in (16.21 m) wingspan of the fixed-wing aircraft, which stretched almost ⅓ of the 188 ft (57 m) length of the small coastal patrol submarine. After U-12 had left the safety of the breakwater, however, the captain realized that the heavy swells they were encountering might swamp the aircraft and endanger the operation, he ordered the immediate launch of the seaplane.

Forstmann flooded the sub's forward tanks and despite the pitching of the boat, Arnauld in command, floated the seaplane off the deck's surface without much difficulty and took off. He had originally intended to rendezvous with the sub, but later decided against it. After gaining sufficient altitude, Arnauld's plane left for the British coast. The German officer apparently flew along the English coastline undetected and then made his way back to occupied Zeebrugge. The experiment had been successful, in the sense that the aircraft had been carried out to sea and had safely floated off the submarine's deck. However, it was obvious that some improvements were needed in the procedure and setup.

Arnauld and Forstmann proposed further development experiments to the German Naval Command, but were vetoed as their project was considered technically impracticable. The plans were kept on ice until 1917, when they were reinvestigated in the hope that they would increase the striking power of new German subs such as the long-range cruise-type Unterseeboote, which were to be equipped with aircraft for scouting purposes - little seaplanes that could be quickly assembled and dismantled onboard and kept in special compartments on deck - but the idea was eventually abandoned as the war came to an end.

Two of the aircraft designs created for that purpose were the biplane Hansa Brandenburg W.20 and low-wing monoplane Luftfahrzeug Gesellschaft L.F.G. Stralsund V.19. The first type was designed in 1917 for use aboard the Cruiser submarines that never went into service. The second model was an experimental plane of the flimsiest construction for use in the calmest of seas.

The British also experimented with the aircraft-carrying submarine concept when HMS E22 was fitted out in a manner similar to the German U-Boat. It was to be capable of launching its two Sopwith Schneider/Sopwith Baby floatplanes in 1916. However, just as in the German experiment, the aircraft were carried outside and the submarine could not submerge without losing them.

World War I / Post-World War I examples

France

Main article: French submarine Surcouf

French submarine Surcouf

Surcouf was a French submarine ordered to be built in December 1927, launched 18 October 1929, and commissioned May 1934. At 4,000 tons (3,600 tonnes) displacement submerged, Surcouf was the largest submarine in the world at the start of World War II. Her short wartime career is laced with controversy and .

Surcouf was designed as an "underwater cruiser", intended to seek and engage in surface combat. For the first part of that mission, it carried an observation float plane in a hangar built into the after part of the conning tower; for the second part, it was armed with not only 12 torpedo tubes but also a twin 8 inches (200 mm) gun turret forward of the conning tower. The guns were fed from a magazine holding 60 rounds and controlled by a director with a 16 ft 6 in (5.03 m) rangefinder, mounted high enough to view a 7 mi (11 km) horizon. In theory, the observation plane could direct fire out to the guns' 15 mi (24 km) maximum range. Anti-aircraft cannons and machine guns were mounted on the top of the hangar.

Italy

Italian submarine Ettore Fieramosca

The Regia Marina (Italian Navy) developed, in the late-1920s, the Ettore Fieramosca, a submarine with a waterproof hangar for a small reconnaissance plane. They gave commissions to the Italian aircraft manufacturers Macchi and Piaggio for two prototypes. The Macchi M.53 and the Piaggio P.8 were developed by 1928, but the program for an Italian aircraft-carrying submarine was cancelled, and the hangar was removed from the submarine in December 1931, before the Ettore Fieramosca was delivered to the Italian navy.

Japan

Main article: Submarine aircraft carriers of Japan

The Japanese applied the concept of the "submarine aircraft carrier" extensively, starting with the J3 class of 1937-38. Altogether 42 submarines were built with the capability to carry floatplanes, one such vessel being the Japanese submarine I-8.

United Kingdom

Main article: HMS M2

After the loss of the heavy gun carrying HMS M1 and the Washington Naval Treaty which restricted the armament of vessels which were not capital ships, the remaining M-class submarines were converted to other uses. By 1927, the M2 had entered service with a waterproof hangar for a Parnall Peto seaplane with folding wings, which could be launched and recovered with the aid of a derrick. In October 1928, she was fitted with a hydraulic catapult which allowed the seaplane to be launched from a ramp on the forward casing. The submarine and her plane could then act as a reconnaissance unit ahead of the fleet, submerging when under threat. The M2 herself was lost in 1932, and plane-launching submarines were abandoned by the Royal Navy.

United States

Main article: USS S-1 (SS-105)

The concept had been studied in the United States since 1922. The American government purchased two Caspar-Heinkel U-1 disassemblable seaplanes for detachment to Anacostia Naval Station for evaluation and testing. Later, one aircraft was lost during an exhibition flight in 1923, but this provided useful technical information.

The United States Navy accepted the construction of 12 submarine-based aircraft at different private enterprises like Cox-Klemin Aircraft (from New York) with their Cox-Klemin XS-1 design (one prototype and five pre-production aircraft) and another six were ordered from Glenn L. Martin Company (from Baltimore) with their design Glenn Martin MS-1, both small disassemblable seaplanes.

Loening XSL-1 in Langley wind tunnel

Both models were tested in the S-1 during October and November 1923. Later, the Cox-Klemm company attempted to develop its design with an XS-2 model, but the Navy lost interest in the concept. In 1931, another similar concept was born when Loening Aircraft Engineering Corporation presented its design the Loening XSL-1 a small flying boat for submarine trials aboard the S-1, but the concept of submarine aircraft carriers was never accepted by the US Navy's submarine service.

News that the British submarine M2 had sunk during aircraft launching trials during 1933, and damage to the XSL-2 during aquatic testings in the Anacostia river area, caused the whole idea of submarine-borne aircraft to be abandoned by the U.S. Navy.

World War II examples

Nazi Germany

Nazi Germany's Kriegsmarine also started development of submarines capable of launching aircraft and ordered four very large "cruiser" U-boats in early 1939. These boats were to be twice as large as any existing U-boat and have a crew of 110. They were intended to carry a single Arado Ar 231 aircraft, but were canceled at the outbreak of war later that year.

Type IX D 2-"Monsun"

Another German long range U-boat was the Type IX D2 "Monsun", used in the Indian Ocean and Far East Area based in Penang (Occupied Malaya) during wartime. To aid such submarines the "Autogyro-Glider" Observation vehicle Focke-Achgelis Fa 330 "Bachstelze" (Water Wagtail) was developed. This vehicle was used in the Indian Ocean and sporadically in the Southern Atlantic, since May–June 1942.

Another plan was the use of Flettner Fl 282A "Kolibri" recon-helicopter version from long range submarines.

Such project implied the special one-place helicopter design were its fuselage was manufactured of welded steel tubing that was sized so that it could be stowed with rotor blades and landing gear removed in a compact area (5.9 ft [1.8 m] in diameter by 18 ft [5.5 m] long) and its pressured hangar for carriage in the U-boat plan.

There is no evidence that any Fl 282 "Kolibri" was deployed on a German submarine in wartime.

Japan

The Japanese applied the concept of the submarine aircraft carrier extensively. Altogether 47 submarines were built with the capability to carry seaplanes. Most IJN submarine aircraft carriers could carry only one aircraft, though a few types could carry two, and the giant I-400 class submarines could carry three.

B1 Type (20 units)

Main article: B1 type submarine

B1 type submarine.

The B1 Type (I-15 Series) submarines (I-15, I-17, I-19, I-21, I-23, I-25, I-26, I-27, I-28, I-29, I-30, I-31, I-32, I-33, I-34, I-35, I-36, I-37, I-38, I-39) were the most numerous type of submarines of the Imperial Japanese Navy during World War II. In total, 20 were made, starting with number I-15, which became the name of the series. These submarines were fast, had a very long range, and carried a single Yokosuka E14Y seaplane, located in a hangar in front of the conning tower, which was launched by a catapult.

The series was rather successful, especially at the beginning of the war. In 1942, I-26 crippled the aircraft carrier USS Saratoga. I-19, on 15 September 1942, fired six torpedoes at the carrier USS Wasp, two of which hit the carrier and crippled it, with the remaining torpedoes damaging the battleship USS North Carolina and the destroyer O'Brien which sank later. I-25 conducted the only aerial bombings ever on the continental United States in September 1942, when an aircraft launched from it dropped two incendiary bombs on a forest near the town of Brookings, Oregon.

AM Type (I-13,I-14)

Main article: Type AM Japanese submarine

The AM (A Modified) type submarine was a large seaplane-carrying submarine, with a hangar space for two aircraft. These giant submarines were originally of the A2 type, but their design was revised after construction started so that they could carry a second aircraft. The seaplanes were to be the Aichi M6A1 bomber carrying 1,760 pounds (800 kg) bombs.

The range and speed of these submarines was remarkable (21,000 nmi/ km at 16 kn/ km/h), but their underwater performance was compromised, making them easy targets. I-13 was sunk on 16 July 1945 by the destroyer escort USS Lawrence C. Taylor and aircraft action from the escort carrier USS Anzio about 550 mi (890 km) east of Yokosuka. I-14 surrendered at sea at the end of the war, and was later scrapped.

Sentoku Type (I-400, I-401, I-402)

Main article: I-400 class submarine

The I-400 class submarine displaced 6,500 tons (5,900 tonnes) and was over 400 ft (120 m) long, three times the size of ordinary submarines. It had a figure-eight hull shape for additional strength to handle the on-deck hangar for housing the three Aichi M6A Seiran aircraft. In addition, it had three anti-aircraft guns and a large deck gun as well as eight torpedo tubes from which they could fire the Long Lance - the largest, longest ranged and most deadly torpedo in use at the time.

Three of the Sen Toku were built, the I-400, I-401, and I-402. Each had four 3,000 hp (2.2 MW) engines and enough fuel to go around the world 1½ times, more than enough to reach the United States from either direction.

The submarines were also able to carry three Sei ran aircraft (the Aichi M6A), each carrying a 1,760 pounds (800 kg) bomb 650 mi (1,050 km) at 360 mph (580 km/h). Its name was combination of sei ("clear sky") and ran ("storm"), literally "storm out of a clear sky," because the Americans would not know they were coming. It had a wing span of 40 ft (12 m) and a length of 38 ft (12 m). To fit the aircraft into the hangar, the wings of the aircraft were folded back, the horizontal stabilizers folded down, and the top of the vertical stabilizer folded over so the overall profile of the aircraft was within the diameter of its propeller. A crew of four could prepare and get all three airborne in 45 minutes, launching them with a 120 ft (37 m) catapult on the fore deck of the giant submarine.

Future designs

There are no known submarine carriers in use today, but several concepts exist that could provide a design in the future allowing an attack force to move entirely underwater, attack without warning, and vanish again. Against this there is the unavoidable fact that a submarine aircraft carrier would be tactically very limited with any attempt to use it to maintain air coverage forcing it to spend large amounts of time on the surface and as a result negating the advantage of being submersible. A marginally more viable role would be carrying out sudden surprise strikes on vulnerable targets. The cost of overcoming the engineering challenges of carrying an aircraft the size of a modern strike fighter combined with such a limited tactical role means that it is unlikely that any navy would consider their construction worthwhile.

There are, however, several projects to develop UAV launch and recovery capabilities. There are three known methods for doing so: launching out of a standard torpedo tube, out of an ICBM vertical launch tube, or from a custom designed unit (probably residing in the sail).^{[citation needed]} The US Navy is a primary driver and customer for this capability, recognising the need for more advanced littoral combat capability, to counter growing area-denial asymmetric threats. The German type 212 submarines will have the capability to launch UAVs.

See also

• Fictional submarine aircraft carriers
• List of submarine-borne aircraft
• Flying submarine
• Airborne aircraft carrier

Further reading

• Terry C. Treadwell: Strike from beneath the Sea: A History of Aircraft Carrying Submarine, Tempus Publishing, Limited, 1999

External links

• Type AM submarine
• Aviation Oddities