in a typical halo exercise, the parachutist will jump from the aircraft, free-fall for a period of time at terminal velocity, and open his or her parachute at an altitude as low as 3,000 feet agl depending on the mission. the combination of high downward speed, minimal forward airspeed, and the use of only small amounts of metal helps to defeat radar and reduces the amount of time a parachute might be visible to ground observers, enabling a stealthy insertion.