American and Japanese became quickly aware of the methods that had been used. By mid-1940, both Japan and Britain had active glider programs. Development then began of even larger gliders such as the Gotha Go 242 (23 trooper) and Messerschmitt Me 321 (130 trooper) to transport heavy armaments in anticipation of Operation Sea Lion and Operation Barbarossa. Gliders were also used by Germany in Greece in 1941. On April 26, 1941, the troops from six DFS 230 gliders captured the bridge over the Corinth Canal accompanied by 40 plane-loads of German paratroopers. (Fortuitously, the British were able to demolish the bridge a few hours later.) Next, General Student then convinced Hitler that Crete could be captured using only airborne troops. Consequently, on May 20, 1941, 500 German transport aircraft carrying paratroopers and 74 DFS 230 gliders took off from the Greek mainland. During the capture of the island, 5,140 German airborne troops were either killed or wounded out of the 13,000 sent. Among the 350 German planes destroyed in the operation, half had been Ju 52s, which seriously depleted the force needed for the invasion of the Soviet Union shortly after. As a result, Hitler vowed never to use his airborne force in such large numbers again. Some German glider operations continued later in the war, some examples being the rescue operation of Benito Mussolini at Gran Sasso and emergency re-supply operations in Russia, North Africa and Eastern Europe towards the end of the war. The Junkers Ju 322 Mammut ("Mammoth") was the largest such glider ever built, but it was never used operationally. Not all military gliders were planned for transport. The Blohm & Voss BV 40 was a German glider fighter designed to attack Allied bomber formations but was not used. British military gliders The British glider development started in mid-1940, prompted by the assault on Eben Emael. Among the types developed were the 28 trooper Airspeed Horsa and the 7-ton capacity General Aircraft Hamilcar cargo glider. The Hamilcar could carry vehicles, anti-tank guns and light tanks into action. The General Aircraft Hotspur – originally planned as a compact assault glider carrying a small number of troops – was used for training the British Army pilots who formed the Glider Pilot Regiment. The Slingsby Hengist was a backup design which was not required when the similar capacity American-built Waco CG-4 (given the British service name "Hadrian") became available