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The Airspeed AS.51 or Horsa Mk I was a World War II troop-carrying glider built by the British company Airspeed and subcontractors and used for air assault by British and Allied armed forces. It was named after Horsa, the legendary 5th century conqueror of Southern Britain.
The use of assault gliders by the British was prompted by the use by Germany of the DFS 230, which was first used in May 1940 to successfully assault the Eben Emael fort in Belgium. Their advantage compared to parachute assault was that the troops were landed together in one place, rather than being dispersed.
With around 28 troop seats, the Horsa was much bigger than the 13-troop American Waco CG-4A (known as the Hadrian by the British), and the 8-troop General Aircraft Hotspur glider which was intended for training duties only. As well as troops, the AS.51 could carry a jeep or a 6 pounder anti tank gun.
The Airspeed 58 or Horsa Mk II had a hinged nose section, reinforced floor and double nose wheels to support the extra weight of vehicles. The tow was attached to the nose rather than the dual wing points of the Mk I.
The Horsa was designed to specification X.26/40 and built from 1940 onwards. It first flew on 12 September 1941. The Horsa featured a high-wing and was of all-wooden construction due to the shortage of other materials and the expendable nature of the aircraft. It was one of the first gliders equipped with a tricycle undercarriage for take-off. On operational flights this could be jettisoned and landing was then on a sprung skid under the fuselage. The wing carried large, 'barn door' flaps, which when lowered made a steep high rate-of-descent landing possible that allowed the pilots to land in constricted areas.
The Horsa was considered sturdy and very manoeuvrable for a glider. Production was by Airspeed and subcontractors including the Austin Motors and the furniture manufacturers Harris Lebus. A total of 3,655 were built. The specification for the gliders had demanded that they were built in a number of sections, and as a result production was spread across separate factories which limited the likely loss in case of German attack.