Of all the humps, runs, and O-courses, the toughest, most physical 3 weeks of training was the Marine Combat Instructor of Water Survival school.
-2000+ meter “strip swims” starting in full camies with pockets open
-“water aerobics” across the width of an Olympic sized pool (underwater swims in full camies, butterfly, crawlstroke, “hands across America”, etc.)
-basic ARC Lifeguard rescues in full gear (including getting attacked by the victim and having to take them under water and apply the appropriate pressure point to get out of the hold)
-50 meter underwater swim (to graduate)
-“water confidence” drills (underwater boot retrieval from 15ft, underwater flips, 20 meter underwater swim, all with either hands or feet bound)
I came out shredded (and skinny). It was brutal but I loved it.
I’ll agree the Marine Corps swim qual is a bastard, if you go all the way. That was the hardest thing I ever did. I have never been that fatigued in my whole life. All the full-pack swims, dragging “dead bodies” across the pool, the Instructors sneaking up behind you and dragging you to the bottom. That was a freaking long day.
Tied for that was the Endurance Course in Quantico, VA in February in about 3 feet of snow (it was so cold and nasty the base was actually shut down, but OCS did not stop). 8 miles of water obsticles, hills, low-crawling, and climbing. It was so cold that by the time we were done our uniforms were frozen on our bodies. No joke, they were hard and crunched when you moved.