The
GI Crawl is the
American English term for an activity familiar to
infantrymen everywhere. It involves lying on your
stomach, holding a
rifle (or other
weapon) off the ground/out of the
mud/above the water by keeping your
elbows on the ground and the hands up in the air to hold the weapon. Then, move forward by kicking with your legs (using the sides of the
knees for purchase) and 'pulling' yourself forward with your elbows and upper arms on the ground.
In films depicting military basic training, the scenes where recruits are moving on the ground, usually under barbed wire with machine-gun fire zipping over their heads - this is what it means to do the GI crawl.
Useful as a civilian when playing Paintball or lazer tag, or trying to sneak into someplace that has its motion sensors or photoelectrics set up a foot off the ground. Adored by laundry detergent companies worldwide.