Falling out of a perfectly good airplane is what airborne soldiers call "work."
While most Marines and soldiers walk or ride into battle, paratroopers pride themselves on getting into harder-to-reach spots, or dropping behind enemy lines. Though military strategists developed plans for their use before 1939, the use of "sky soldiers" was really perfected during World War II.
Perhaps the most famous use of paratroopers was during the Normandy invasion of 1944, when more than 13,000 airborne troops dropped from the sky behind German positions in France. Today, the U.S. and other countries still maintain airborne soldiers, or train up their special operations forces in airborne operations.
A common trope among the airborne is that it's crazy to "jump out of a perfectly good airplane." But if you think it's crazy, then you're probably just a leg (that's airborne talk for regular-old ground troops).
Check out 12 photos of U.S. and other airborne troops: