Squash, sometimes referred to as jet-propelled chess, has a long history of weeding out the also-rans, leaving only the most physically and mentally tough to slug it out.
Each student takes part in regularly scheduled activities in self-reliance such as carrying bricks, planting bananas, digging foundations, watering and weeding his own trees, etc.
There was no commando, airborne or other selection procedure, although there was some weeding out of less fit personnel during training for operations.