Military parachutes for use by humans (both paratroopers and distressed aircrew) tend to be of simple round or (more recently) cruciform design:
(Image by the United States Army, via Wikimedia Commons.)
These are simple drag parachutes, generating no lift. In contrast, sport parachutists nowadays almost invariably use much-more-advanced rectangular or elliptical ram-air parachutes, which generate much lift and relatively little drag:
Military use of ram-air parachutes is essentially limited to display teams.
This seems rather odd, given that lifting ram-air parachutes:
- allow for much lower descent rates (and, thus, softer touchdowns - something which would be especially important for paratroopers, who jump with lots more heavy gear than sport skydivers, and ejectees, who are likely already injured, and, thus, tend to have less ability to tolerate hard touchdowns) than drag parachutes, due to their greater aerodynamic efficiency;
- allow their users to glide considerable horizontal distances once deployed and can be manoeuvred nimbly, which would:
- allow paratroops to be dropped some distance from a target and glide silently in;
- allow wind-induced dispersal of a large paratroop unit to be negated;
- allow paratroops to manoeuvre to land in a suitable area or to evade antiaircraft fire;
- allow ejectees to glide towards territory controlled by friendly forces and/or terrain with the least potential for further exacerbating any injuries to the ejectee.
So why do military users stick with drag parachutes rather than moving to lifting ram-air parachutes?