Bell's XH-40 prototype first flew on 22 October 1956 and entered production in the same year as the HU-1A. The "HU" designation spawned the famous "Huey" nickname, although the re-alignment of US service designations in 1962 changed it into the familiar UH-1. The UH-1 made the theory of air cavalry practical, as the new tactics called for US forces to be highly mobile across a wide area. Unlike before, they would not stand and fight long battles, and they would not stay and hold positions. Instead, the plan was that the troops carried by fleets of Hueys would range across the country, to fight the enemy at times and places of their own choice. It soon became clear that the unarmed UH-1 troop helicopters were vulnerable against ground fire from Viet Cong and NVA troops, particularly as they came down to drop their troops in a landing zone. Without friendly support from artillery or ground forces, the only way to pacify a landing zone was from the air, preferably with a machine that could closely escort the transport helicopters, and loiter over the landing zone as the battle progressed. By 1962 a small number of armed HU-1As (UH-1As) were used as escorts, armed with multiple machineguns and rocket mounts.