In World War II, airborne units were really in their infancy. The Germans pioneered their use in combat, and the United States built perhaps the largest airborne force in the world, with five airborne divisions.
But these divisions had a problem. There weren't many planes to transport them for large-scale airborne ops. Today, most transports used in airborne operations have rear ramps for loading cargo (like, jeeps and artillery). Back then, they didn't.
The C-47 Skytrain was based on the DC-3 airliner. The C-46 Commado was also based on an airliner.
A C-47 takes off, towing a Waco CG-4 glider during Operation Market Garden. (Imperial War Museum photo)
Yeah, paratroops could be dropped, but they could be scattered (thus creating the rule of the LGOPs). How would they drop the heavier equipment, and keep the crews together? The answer came with the development of gliders. Nazi Germany and the Soviet Union pioneered the use of them, but the U.S. and Great Britain built lots of them.
According to the National World War II Glider Pilots Association's web site, the United States built over 13,000 CG-4A Waco gliders. Each of these gliders could carry 15 troops, or a Jeep and four paratroopers, a trailer, up to 5,000 pounds of supplies, an anti-tank gun plus operators, or a 75mm artillery piece and its crew.
Troops with the 504th Parachute Infantry Regiment load some heavy firepower onto a CG-4 glider. (US Army photo)
The U.S. also used British Horsa gliders to carry even larger groups of troops (up to 30 in a glider) or bigger amounts of supplies. Over 300 of these gliders were used on D-Day, one of those instances where the arsenal of democracy had to borrow a plane made by an ally.
About 6,500 glider pilots were trained during World War II, taking part in eight missions from Sicily to Luzon. In the 1950s, advancements in transport aircraft, both fixed-wing and rotary-wing, led to the glider units being deactivated in 1952. But the gliders helped deliver firepower, troops, and supplies during World War II – when that ability was needed.
The video below shows how gliders were used during the Normandy invasion.