If one lesson was learned above all others from World War One it was that in any future war it would be the side whose technology was superior that would most likely be the winner. This was most true of two of the new forms of war that emerged in that horrific conflict; the aircraft and the submarine. History considers the role of the aircraft in World War One as something of a side-note in the overall scheme of things. The same cannot be said for the submarine however which dramatically highlighted how vulnerable the traditional grand fleets of the imperial powers were to this new menace.
The key to this success was the submarine’s ability to go undetected for extended periods of time and some forward thinkers in the Admiralty recognised the potential use of the submarine in the reconnaissance role. Unfortunately the submarines of the First World War and the immediate post war period lacked the technology to be truly effective in the role; they being limited to look-outs in the coning tower while on the surface where the submarine was both visible and vulnerable. When submerged the submarine was limited further to the one eyeball of the officer-of-the-watch who had to peer through a periscope to see the world outside.
To many, including the newly formed Royal Air Force who still controlled the Royal Navy’s aviation elements, the aircraft was the solution. This could not only track ships from a safe altitude but could go ashore and carry out reconnaissance in advance of a landing force. Aircraft had been flying in the spotter role from the decks of warships since before the start of the war and combat experience had made Royal Navy spotter crews quite proficient. However aircraft carrying ships had to be quite large in order to accommodate the aircraft and supporting equipment which increased their chances of detection.
With these problems in mind, towards the end of the First World War some Royal Navy officers began to flirt with the idea of combining the stealth of a submarine with the reconnaissance capabilities offered by naval aviation. They proposed building a submarine that could sail ahead of the main fleet undetected, surface to launch its aircraft and then dive again once it was away only to surface later to recover the aircraft and assimilate the results of its mission. This had the advantage of not exposing any large warships to enemy fire whilst on a reconnaissance mission as had been the case during the war and the aircraft’s speed also reduced the enemy’s ability to respond.
There were some notable obstacles in the way of the plan however. Firstly a submarine is an extremely small and cramped vessel and so in order to be able to store as well as launch and recover an aircraft it was going to have be constructed on a much larger scale than before. A new aircraft was also going to have to be designed that could operate from the submarine. Another problem is that submarines were notoriously poor seakeepers when operating on the surface and this would make hoisting an aircraft difficult in all but the best of conditions. Nevertheless the gains seemed to outweigh the risk and plans were put in to place to start development work while the Air Ministry issued specification 16/24 which called for a suitable aircraft to be built to operate off the submarine.
The Royal Navy already had a submarine it felt was suitable for modification in to the world’s first submersible aircraft carrier. The M-class was one of the Royal Navy’s efforts to build the underwater equivalent of the Dreadnoughts; Britannia ruled on top of the waves so she might as well rule underneath them too. This ambition met with little success and produced among others the K-class submarine. This submarine class has become legendary in the Royal Navy Submarine Service but for all the wrong reasons. It was something of a behemoth in its day and utilised steam power when travelling on the surface to charge its batteries. The class is remembered for having an appallingly high accident rate leading to crews calling them the Kalamity-class with six being lost in accidents while only ever having fired a single torpedo at the Germans throughout the whole war and even then it failed to explode. In one incident the future King George VI was onboard one of the class when it carried out a diving test but became unable to surface until, after frantic efforts by the crew, the main ballast was blown and it rose to the surface.
The K-class gave way to the M-class which had a much better although not exactly spectacular career. Like the K-class the M-class was a beast of a submarine for the First World War displacing nearly 1600 tons while on the surface. While the M-class did carry torpedoes like other submarines it was also one of a number of designs that featured a heavy main gun, in this instance a 12-inch Mark IX gun. This might seem strange to modern eyes but in the early years of the First World War torpedoes were notoriously unreliable and it was felt that the submarine could be just as successful by carrying out surprise attacks with a heavy gun armament. Over time torpedoes were improved and the vulnerability of such submarines became more apparent.
In 1925 the two remaining M-class submarines, HMS M-2 and M-3 (British submarines still didn’t have names at this point), were withdrawn from frontline service and relegated as test vessels. HMS M-2 was therefore taken in hand to become the first aircraft carrying submarine with work being carried out to remove the gun armament and construct a water tight aircraft hangar in its place along with the necessary launching facilities. A derrick was fitted which would lift the aircraft off the deck and put it in the water for launch and then recover the aircraft after its mission had been completed. The work was completed in 1927 and sea trials commenced shortly after.
At the same time that work on the submarine was commencing tests were being carried out with the aircraft that would operate from it. George Parnall and Co. is a relatively unheard of aircraft company today but between the 1920s and 1940s the company built a number of successful military and civil aircraft. To demonstrate just how primitive aircraft technology was back in these very early years the company actually started life as a family run wood-working firm with very little aeronautical experience behind them. Nevertheless they persevered and began building aeroplanes using their skills with wood to great advantage while hiring the necessary engineers to work on the engines and aerodynamics. Parnall responded to the Air Ministry’s curious specification with an aircraft that would become known as the Peto.
The Peto was far more complicated than any of the company’s previous designs but Parnall knew that if the Royal Navy’s dream of submarine-based aircraft bore fruition then it was possible for the company to establish a monopoly early on in designing and building the aircraft. Even by the standards of the day the aircraft was miniscule being just 22ft 6in long and having an upper wingspan of 28ft when not stowed away (the lower wing was slightly shorter). The aircraft was constructed in a combination of wood, fabric, aluminium and steel while power was derived from a 128hp Bristol Lucifer engine. Flight testing revealed that the aircraft handled well with delightful characteristics but the Lucifer engine felt underpowered and following a mishap with the first prototype it was decided during repairs to replace the engine with a 138hp Armstrong-Siddeley Mongoose IIC engine which gave the aircraft a sprightlier feel. The Admiralty were pleased with the aircraft and eager to begin tests with it operating off their newly modified submarine.
Early tests showed that while the concept was feasible the task of lifting the aircraft in and out of the water was quite laborious and left the submarine vulnerable. Therefore in 1928 HMS M-2 went back to the builder’s yard and work began on fitting the vessel with a hydraulic catapult protruding out from the watertight hangar. The idea was that the submarine could surface, the doors to the hangar open, the aircraft pulled out and its wings unstowed before immediately being catapulted in to the air. This would save a great deal of time but the aircraft would still have to be lifted by its derrick back aboard after the flight. The catapult proved a success and the Peto showed no signs of difficulty in operating from it.
Trails with HMS M-2 and her Peto continued as the 1930s dawned but there were now many doubters of the whole project who felt that the range and endurance of newer aircraft operating off an aircraft carrier was increasing to the point where they could venture far in advance of the fleet. This would negate the need for reconnaissance by a submarine launched aircraft. Nevertheless while the two sides of the argument fought the Royal Navy made much use of the unique vessel for publicity purposes going as far as to produce a public information film for viewing in the cinema.
On January 26th 1932 HMS M-2 left Portland for an exercise in West Bay off the Dorset coast. At 1011hrs the submarine signalled that she was beginning her dive. Just over an hour later a passing merchant ship observed a submarine diving stern first but the crew, unfamiliar with how submarines worked, failed to realize just what they were seeing – the sinking of HMS M-2. As a result they did not report what they saw until sometime after when it was realized the submarine was missing.
After several days of searching, divers stumbled upon the wreck of the submarine laying relatively intact on the ocean floor. Investigation revealed that the hangar doors had been opened too early during surfacing drills and the submarine quickly flooded as a result. There were no survivors from her 60 crew. A short time later an effort to salvage the submarine was made and despite it being lifted some 20ft off the ocean floor a storm disrupted operations and the wreck broke free before settling on the bottom for a second and last time. The wreck remains there to this day.
Looking back at the whole project the Admiralty decided that to pursue the concept further would be a waste of time and resources and so the Royal Navy ended its flirtation with submarine-launched aircraft. Other countries were still intrigued by the concept however most notably Japan where an up and coming naval officer named Isoroku Yamamoto envisioned submarine-based attack aircraft being launched undetected close to an enemy shore to bomb important targets. His vision ultimately lead to the awe-inspiring I-400 series of aircraft-carrying submarines that fortunately arrived too late in the Second World War to have an impact on world events.
In one final twist to the whole concept, the advent of miniature Unmanned Aerial Vehicles (UAV) and even the reconnaissance configured cruise missile may see the resurfacing of the “underwater aircraft carrier” at least in an unmanned form.