The Horsa was considered sturdy and very manoeuvrable for a glider. Production was by Airspeed and subcontractors including Austin Motors and the furniture manufacturers Harris Lebus. A total of 3655 were built. The specification for the gliders had demanded that they were built in a number of sections, and to use facilities not needed for more urgent production, and as a result production was spread across separate factories which limited the likely loss in case of German attack.
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 Horsa was first used operationally on the night of 19/20 November 1942 in the unsuccessful attack on the German Heavy Water Plant at Rjukan in Norway (Operation Freshman). The two Horsa gliders, and one of the Halifax tug aircraft, crashed in Norway due to bad weather. All 23 survivors from the glider crashes were executed on the orders of Hitler, in direct breach of the Geneva Convention which protects POWs from summary execution. After this Hitler called the airborne soldiers "Red Devils" due to their maroon berets. The name stuck with them.
On 10 July 1943, 27 Horsas were used in Operation Husky, the invasion of Sicily. Large numbers were subsequently used in Operation Tonga and the American airborne landings in Normandy (Battle of Normandy), Operation Dragoon (southern France), Operation Market Garden (Arnhem) and Operation Varsity (crossing the river Rhine). In Normandy, the first units to land in France did so by Horsas, capturing Pegasus Bridge.
On operations they were towed variously by Stirling, Halifax, Albemarle, Whitley and Dakota tugs, using a harness that attached to both wings. The pilots were usually from the Glider Pilot Regiment, part of the Army Air Corps, although Royal Air Force pilots were used on occasion. The Horsa was also used in service by the USAAF. On 5 June 2004, as part of the 60th anniversary commemoration of D-Day, Prince Charles unveiled a replica Horsa on the site of the first landing at Pegasus Bridge, and talked with the original pilot of the aircraft, Jim Wallwork.