Parachute jumping is an intense experience, and military jumps can be particularly stressful. The intended purpose is to deploy the entire contingent of soldiers onto the drop zone very quickly in order to achieve a concentrated force on the ground as rapidly as possible. There is very little comparison to sport parachuting in which the object is to enjoy the experience.
The aircraft typically used for airborne assault operations are usually cargo planes, unarmed, relatively slow, and flying at altitudes below any requirement for supplemental oxygen. There are two "jump doors" located toward the rear of the cargo areas, one on each side of the aircraft. The paratroopers (or trainees) are arranged in "sticks", typically about 25 or so along each side of the plane, sitting in folding web seats for the trip. On approach to the designated drop zone there will be a warning order conveyed with a shout and hand signals, typically indicating six minutes until the jump is to begin.
The next command (again with hand signals) is "stand up", and the lines of soldiers rise from the web seats. Remember that the aircraft is maneuvering to maintain a direct approach, and the winds aloft and atmospheric conditions may affect anyone's abilities to stand easily. Having a full body harness for the parachute, the parachute pack on the back, a reserve parachute at the belly area, an equipment bag attached to the harness around knee level, and your weapon slung securely (usually about 60 lbs. or so of gear), none of these things make it any easier, and you are always in close contact with others in a moving airplane.
The next command is "hook up", the hand signal indicating the need to connect your static line to the overhead cable.
That is followed by "check equipment". Each soldier will visually and manually check his buddy's gear, physically yanking and tugging at every part of the harness, face to face, then on the back. Assuming everything is right, there will be a slap on the shoulder. Then everyone faces to the rear of the plane holding onto the static line clipped overhead and in close contact throughout the line.
On final approach the jumpmaster will announce "stand in the door". The first soldier in line (traditionally the more senior personnel, platoon sergeants and/or platoon commanders) will step to the jump door, grip the opening with both hands and prepare to leap forward into the slipstream of air passing the fuselage (perhaps 90MPH or more).
On command of the (hopefully well-experienced) pilot, the command will be given to "GO" with a strong slap on the shoulder. The first guy in line will throw himself out into the slipstream and the next man will stand in the door.
That will continue at a rate of about one soldier out the door every couple of seconds until the entire stick is in the air, then the jumpmaster will follow as the last jumper.
The primary objects of the exercise are to deploy the entire contingent very quickly, usually under a minute for 25 to 27 men on each side of the aircraft to go out the door. It is important that everyone remain in close proximity to each other, rather than to have people widely scattered on the drop zone. A concentrated and cohesive team on the ground is the immediate goal.
Combat jumps are done at the lowest possible altitude, given weather conditions and terrain. No one wants to be riding a parachute too long while entering an area inhabited by other folks who don't want uninvited guests, and have weapons to make a contest of the situation. At minimum altitudes the actual time from exiting the airplane until on the ground can be as short as 30 seconds or so, perhaps a minute. Definitely not a long, lazy, enjoyable ride down as might be the case in sport parachuting.
Leaving the aircraft and entering the slipstream is an experience commonly referred to as "prop blast". The moving air (actually the aircraft and human bodies moving through the air) is a physical force that slams you, and can twist your body, tumble your body, and completely disorient the mind. As this happens your static line is engaging, then ripping open the pack around your parachute and deploying the canopy. As the canopy opens there is a sudden braking effect, filling with air and quickly dragging the jumper from 90 or 100MPH forward velocity to about zero forward velocity. Always best to have your harness properly and snugly adjusted, particularly the two web straps passing around the groin area, as all those forces are suddenly applied to the body.
Very quickly you find yourself transitioning from a very loud aircraft and high velocity blasting air into a much quieter and more peaceful atmosphere. The noise of the airplane moves away very quickly. There may be some sense of motion from swaying back and forth under your canopy, and as you look down there is a definite sense of downward velocity as the ground is quickly coming up at you.
The old T-10 parachute is not a sport model. Very little controlled steering. It is possible to pull downward on one side of the suspension harness and induce a bit of spiral effect that (hopefully) keeps you headed toward a nice place to land, or away from ugly terrain features you might hope to avoid. Maybe. Never hurts to try!
As the ground reaches up to reclaim you there is plenty to think about. Your equipment bag is attached at waist level with a release to drop it free on a strap (about 15 or 20 feet long, IIRC); let it go too soon and it will drop to the end and yank hard on your harness, potentially affecting your body position as you make your final approach to the ground. Ideally, release it to fall directly to the ground without distraction or disorientation.
Then it is all about feet and legs together, knees flexed to absorb the impact, and the tuck and roll in whichever direction is required by ground wind or oscillation in your harness under the canopy. As soon as your weight leaves the harness the canopy should quickly collapse, but may just as easily capture any ground breeze with enough energy to drag you over the ground. That is when the quick-release feature of the harness is needed, a simple connection at about center chest area that can be struck with one hand to disengage the four primary straps of the harness and release you from the contraption. Grabbing one of the risers will cause the canopy to deflate and fall to the ground, then it can be bundled and rolled up for recovery.
There you are! Quick and easy! What could possibly go wrong? Sure, you might end up in a tree, or you might break and ankle or slam your tailbone hard enough to cause a compression fracture in the lumbar spine, but hardly anybody ever breaks his neck or ends up in a power line.
It seems that I overlooked the possibility of leaving the aircraft and mentally counting out the 4 seconds that usually allow the parachute to deploy, then not experiencing the joy of full canopy inflation. At that point the human body would essentially be in free-fall mode, rapidly accelerating toward Mother Earth. Time to engage the reserve parachute, a much smaller unit mounted about belly height with a handy D-shaped ripcord to tear open the pack and (hopefully) deploy a little 15-foot mini-parachute intended to slow you down enough for the ambulance to find you easily on the ground. That is, if your thinker continues to function after the shock of not having a functioning primary parachute!
Interesting memories:
1. Primary parachute deployed as expected, but accompanied by a loud cracking sound. Looked up and saw that one panel of the parachute had ripped open from bottom to top. This allowed air to escape and caused both a more rapid speed to the ground and a wide spiraling path. Bit of a hard landing with less than optimal control. (Parachutes are not "single use items", they are reused many times).
2. Watched two other guys converge, one directly over the other. This caused the upper parachute to lose inflation and the soldier ended up on the canopy of the other guy beneath him. He had the presence of mind to pull himself off the side, dropping away, and both guys landed safely. Enough altitude to make it work, that time anyway.
3. One trainee exited the aircraft on command, tumbled in the prop blast, then found his head and helmet stuck in the apex of the next guy's inflating parachute. Then his own chute inflated, yanked him clear, somehow tore the helmet from his head without breaking his neck.
4. Parachute riggers hangar at Fort Benning, where the riggers packed each parachute on long work tables, hundreds of rubber bands to contain all the suspension lines, and sewing each pack shut to allow it to rip open as the static line pulled the parachute out. Over the big doors was a banner announcing "IF IT DOESN'T WORK BRING IT BACK".
Enough old memories for one night.