[lucasjung]

The SEALs do both: they are very picky about who gets into BUD/S, BUD/S weeds out all but the best, and then they continuously train to stay the best.

I actually believe that the USMC's formula for success doesn't scale without limit. They are way smaller than the Army, and I'm sure that's a big part of how they are able to maintain the kind of cohesive culture needed to sustain excellence.

Also, even during the draft era, the Marines had another tool that you didn't consider: attrition. I don't mean the combat kind, I mean washing out the people who can't cut it. It's amazing how thoroughly they can transform a young person, but even so there are some people that just aren't good enough, and the Marine Corps has always been the most willing of all services to get rid of dead weight. So it's not selection vs. training, it's a three-way combination of selection, training, and attrition.