Gliders were used by both sides to deliver troops and equipment to locations where traditional aircraft couldn't go. Because they were unpowered, gliders were particularly good at delivering their cargo undetected behind enemy lines.
The Treaty of Versailles prevented Germany from having an air force, so German aviators formed glider clubs to retain their flight skills and train new pilots. From that came increased interest in gliders as military weapons. Large gliders were found to be superior to parachute landings in efficiently delivering large numbers of troops and equipment to a specific site.
One of the first significant German military gliders to be developed was the DFS 230, which could carry nine men. It was first test-flown in 1937 and proved to be quite useful. A glider commando force was formed in 1938, and production of the DFS 230 was greatly increased. By 1943, more than 1,500 of the craft had been made. During the German campaign of 1940 in France and the Low Countries, gliders were used to take Fort Eben Emael on the Belgian border. Gliders were also used during the German invasion of Crete in 1941, to bring supplies to besieged German troops in the Soviet Union, and to rescue Benito Mussolini in September 1944.
Larger and better gliders were soon created by the German air force, including the Gotha Go 242, which could carry 21 men, and the massive Messerschmitt Me 321 Gigant, which could carry 130 soldiers, though it was used primarily to transport cargo.
The U.S. Army Air Forces ignored the glider concept until Germany proved the planes' usefulness in a number of important airborne assaults in 1940 and 1941. Military aviation experts began to explore glider design in February 1941, and two distinct designs were eventually mass-produced: the CG-4A, which could carry thirteen men, and the CG-13, which could carry thirty. More than 14,000 of these gliders were produced over the course of the war.
The Allies used gliders to deliver troops and equipment during several crucial campaigns, including the capture of Sicily in 1943, the Normandy invasion in June 1944, and the Rhine crossings in 1945. Gliders were used sparingly in the Pacific because of the distances between bases and their objectives, as well as a shortage of transport craft.
Britain, the Soviet Union, and Japan all used gliders to varying degrees over the course of the war. The Soviet Union even designed a glider-bomber known as the PB, though the craft never left the drawing board.