The Airspeed AS.51 Horsa was a British troop-carrying glider used during the Second World War. It was developed and manufactured by Airspeed Limited, alongside various subcontractors; the type was named after Horsa, the legendary 5th-century Germanic conqueror of southern Britain.
Having been greatly impressed by the effective use of airborne operations by Germany during the early stages of the Second World War, such as during the Battle of France, the Allied powers sought to establish capable counterpart forces of their own. The British War Office, determining that the role of gliders would be an essential component of such airborne forces, proceeded to examine available options. An evaluation of the General Aircraft Hotspur found it to lack the necessary size, thus Specification X.26/40 was issued. It was from this specification that Airspeed Limited designed the Horsa, a large glider capable of accommodating up to 30 fully equipped troops, which was designated as the AS 51.
The Horsa was used in large numbers by the British Army Air Corps and the Royal Air Force (RAF); both services used it to conduct various air assault operations through the conflict. The type was used to perform an unsuccessful attack on the German heavy water plant at Rjukan in Norway, known as Operation Freshman, and during the invasion of Sicily, known as Operation Husky. Large numbers of Horsas were subsequently used during the opening stages of the Battle of Normandy, being used in the British Operation Tonga and American operations. It was also deployed in quantity during Operation Dragoon, Operation Market Garden, and Operation Varsity. Further use of the Horsa was made by various other armed forces, including the United States Army Air Forces.
Development Background In the early stages of the Second World War, the German military demonstrated its role as a pioneer in the deployment of airborne operations. These forces had conducted several successful operations during the Battle of France in 1940, including the use of glider-borne troops during the Battle of Fort Eben-Emael.Flanagan 2002, p. 6. Having been impressed by the performance and capabilities of German airborne operations, the Allied governments decided that they would also form their own airborne formation.Harclerode 2005, p. 197. As a result of this decision, the creation of two British airborne divisions came about, as well as smaller-scale units.Harclerode 2005, p. 107. On 22 June 1940, the British airborne establishment was formally initiated when the Prime Minister, Winston Churchill, directed the War Office in a memorandum to investigate the possibility of creating a corps of 5,000 parachute troops.Otway 1990, p. 21. During 1941, the United States also embarked on a similar programme.Mondey 2002, p. 14.
While the equipment for the airborne forces was under development, it was decided by War Office officials that gliders would be an integral component of such a force. It was initially thought that gliders would be used to deliver paratroops. Transport aircraft would both carry paratroops and tow a glider with a second party of troops. The idea arose as a response to the severe shortage of transport aircraft in the early part of the war, as in this way the number of troops that could be dropped in an operation by a given number of transport aircraft would be greatly enhanced. The empty gliders would be towed back to base.Manion 2008, p.28
However, thinking eventually evolved into using gliders to land both troops and heavy equipment in the theatre of operations.Flint 2006, p. 15. The first glider produced was the General Aircraft Hotspur, which first flew on 5 November 1940.Lynch 2008, p. 31. Several problems were found with the Hotspur's design, the worst being its inability to carry sufficient troops. It was believed that airborne troops should be landed in larger groups than the eight that the Hotspur could carry, and that the number of towplanes required would prove to be impractical. There were also concerns that the gliders would have to be towed in tandem, which would be extremely hazardous at night or through cloud.Smith 1992, p. 13.
Accordingly, it was decided that the Hotspur would be used only as a training glider,Otway 1990, p. 23. while British industry continued with the development of several different gliders, including a larger 25-seater assault glider, which would become the Airspeed Horsa. On 12 October 1940, Specification X.26/40 was issued, calling for a large assault glider.Flint 2006, p. 35. The specification required the use of wood where possible to conserve critical supplies of metal.Mrazek 2011, p. 331. Airspeed would designate the Horsa the AS.51.
Airspeed assembled a team headed by aircraft designer Hessell TiltmanMrazek 1977, pg. 70. whose efforts began at the de Havilland technical school at Hatfield, Hertfordshire, before relocating to Salisbury Hall, London Colney. The Horsa was to have had paratroopers jumping from doors on either side of the fuselage, while the glider remained under tow, while combat landings would have been secondary. The widely set doors enabled simultaneous egress, as well as for troops to fire on nearby enemies while still in the glider. For this they were provided with several firing points in the roof and tail. That idea was dropped, and it was decided that the glider would simply land troops.
Production In February 1941, an initial order was placed for 400 gliders and it was estimated that Airspeed should be able to complete the order by July 1942.Smith 1992, p. 14. Early on, inquiries were made into the possibility of a further 400 being manufactured in India for the use of Indian airborne forces, however, this plan was abandoned when it was discovered the required wood would have to be imported into India. Seven prototypes were ordered with Fairey Aircraft producing the first two prototypes, which were used for flight testing, while Airspeed completed the remaining prototypes that were used in equipment and loading tests. On 12 September 1941, the first prototype (DG597), towed by an Armstrong Whitworth Whitley, made its first flight, 11 months after the specification was issued.Flint 2006, p. 56.
As specified in Specification X3/41, 200 AS 52 Horsas were also to be constructed to carry bombs. A central fuselage bomb bay holding four or two bombs was fitted into the standard Horsa fuselage. The concept of towing bombs was dropped as other bombers became available, resulting in the order for the AS 52 being cancelled.Bowyer 1976, p. 37.
In early 1942, production of the Horsa commenced; by May 1942, some 2,345 had been ordered by the Army for use in future airborne operations. The glider was designed from the outset to be constructed using components and a series of 30 sub-assemblies required to complete the manufacturing process. Manufacturing was intended primarily to use woodcrafting facilities, which were not needed for more urgent aviation production, and as a result, production was spread across separate factories, which consequently limited the likely loss in case of German attack. The designer A. H. Tiltman said that the Horsa "went from the drawing board to the air in ten months, which was not too bad considering the drawings had to be made suitable for the furniture trade who were responsible for all production."
The initial 695 gliders were manufactured at Airspeed's factory in Christchurch, Hampshire;Thetford 1968, p. 588. production of the remainder was performed by an assortment of subcontractors. These included Austin Motors, and a production group coordinated by the furniture manufacturers Harris Lebus.Lloyd 1982, p. 22. These same contractors would produce an improved model of the glider, designated as the AS.53 Horsa Mk II, while none would be manufactured by Airspeed themselves. The Horsa Mk II had been specifically designed for the carriage of vehicles, featuring a reinforced floor and a hinged nose section in order to accommodate such use. Other changes included the adoption of a twin nosewheel arrangement, a modified tow attachment and an increased all-up weight of .
As a consequence of the majority of subcontractors not having available airfields from which to deliver the gliders, they sent the sub-assemblies to RAF Maintenance Units (MUs), who would perform final assembly themselves; this process has been attributed as being responsible for the widely varying production numbers recorded of the type. Between 3,655 and 3,799 Horsas had been completed by the time production ended.
Design
The Airspeed AS.51 Horsa was a large troop-carrying glider. It was capable of transporting a maximum of 30 seated fully equipped troops; it also had the flexibility to carry a Jeep or an Ordnance QF 6-pounder anti-tank gun. The Horsa Mark I had a wingspan of and a length of , and when fully loaded weighed .Smith 1992, p. 15. The later AS 58 Horsa II featured an increased fully loaded weight of along with a hinged nose section, reinforced floor and double nose wheels to support the extra weight of vehicles. The tow cable was attached to the nose wheel strut, rather than the dual wing points of the Horsa I. The Horsa was composed largely of wood; it was described by aviation author H. A. Taylor as being: "the most wooden aircraft ever built. Even the controls in the cockpit were masterpieces of the woodworker's skill".Mrazek 2011, p. 336.
It was considered to be sturdy and very manoeuvrable for a glider. The design of the Horsa adopted a high-wing cantilever monoplane configuration, being equipped with wooden wings and a wooden semi-monocoque fuselage. The fuselage was built in three sections bolted together, the front section held the pilot's compartment and main freight loading door, the middle section was accommodation for troops or freight, the rear section supported the tail unit.
The fuselage joint at the rear end of the main section could be broken on landing to facilitate the rapid unloading of troops and equipment, for which ramps were provided.Morgan 2014, p. 59. Initially the tail was severed by detonating a ring of Cordtex around the rear fuselage. But this was thought to be hazardous, especially if detonated prematurely by enemy fire.Manion (2008), p.33 In early 1944, a method of detaching the tail was devised that used eight quick-release bolts, and wire-cutters to sever the control cables.
The wing carried large "barn door" flaps which, when lowered, made a steep, high rate-of-descent landing possible—this performance would allow the pilots to land in constricted spaces. By employing a combination of the flaps and pneumatic brakes, the glider could be brought to a stop within relatively short distances. The Horsa was equipped with a fixed tricycle landing gear and it was one of the first gliders equipped with a tricycle undercarriage for take off. On operational flights, the main gear could be jettisoned and landing was then made on the castoring nose wheel and a sprung skid set on the underside of the fuselage.
The pilot's compartment had two side-by-side seats and dual controls, all of which being contained within a large Plexiglas nose section. Initially, the cockpit would be outfitted with internal telephone systems that allowed for communication between the pilots of the glider and tug aircraft while connected; however, this was replaced on later-built models by radio sets instead, which had the advantage of being able to maintain contact after detaching. Aft of the pilot's compartment was the freight loading door on the port side; the hinged door could also be used as a loading ramp. The main compartment could accommodate 15 troops on benches along the sides with another access door on the starboard side. Supply containers could also be fitted under the centre-section of the wing, three on each side.