Had a chance to do pool work with a 20th group soldier (initial W.M.) few weeks ago. He was heading to Key West. We were working mainly to smooth out side stroke, but we also did drown proofing, and underwater swim. I showed him the "key hole" stroke, paying special attention to feet kicking as hands are by the ears (timing!). Here are good visuals of the technique:
http://www.youtube.com/watch?v=qMwpNHof0hM
http://www.youtube.com/watch?v=jxpNqGDY-F0
By the 2nd day, he was pulling 50 yards+ going back and forth right after entering the pool, no warm up, nothing, which made my jaw literary dropped
. Keep in mind he is not a good swimmer, hardly ever swim, and at this point, he's been swimming for only about 2, 30 min sessions. Last year, a PJ trainee did 75 yards plus which was impressive, but he spent 30 min+ warming up and building up the lung capacity. The SF guy told me the last 30 yards was pure will power. Such testament of mind over matter is an ever-present motivation for my journey towards SF.
Eagle is right, hug the bottom. A Marine Recon instructor told me it's got something to do with water density, and how you're almost literary pushing off the bottom (solid surface as opposed to just fluid), which equals greater propulsion.