The M113 was developed to provide a survivable and reliable light tracked vehicle able to be air-lifted and air-dropped by C-130 and C-141 transport planes. The original concept was that the vehicle would be used solely for transportation, bringing the troops forward under armor and then having them dismount for combat, after which the M113 would retreat to the rear. Entering service with the U.S. Army in 1960, the M113 required only two crewmen, a driver and a commander, and carried 11 passengers inside the vehicle. Its main armament was a single .50-caliber (12.7 mm) M2 Browning machine gun operated by the commander.