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(I Googled up this interesting discussion fragment. For the record, I've done it from 50 feet in a tower. I have swum out of the escape trunk of a submarine during routine training, but with SCUBA. --Travis)

Back in ancient days (before the fire burnt the water filled escape tower in '68) all submariners made qualification escapes from a 100 ft tank of water that was the tallest structure in the New London area (which was the reason the fire trucks could not stop the HP air/ hydraulics fire). Two types of escape -- a free escape with only a lifejacket, and the lifejacket plus Stenke Hood (a transparent plastic bag over the head with an air bubble - so you breathed (out obviously) into a "normal" environment instead of venting directly into water)

Candidates would enter an escape trunk mockup at 50 ft depth, flood down, equalize pressure, open hatch and exit. Free divers would make a surface dive to your depth and escort you to the surface as your (partially) inflated lifejacket sent you upwards. You would make the trip with mouth open, and travel like a rocket because of the buoyancy. When reaching the surface you would rise to about the knee level and then sink back -- you were moving fast!!. Bends is not a problem because you did not have much time at pressure so you could make a fast surfacing, something that SCUBA divers should not try because they are quickly saturated at depth. Tank depth was limited because of ompression problems for escorting free divers placed time limits on their workday that shortened with depth.

The Stenke Hood was used from 75 ft, and was just boring. Same operations as before, but hood presence caused loss of fear associated with the free ascent. Dr Stenke had the record for free ascents at that time (750 ft) for the escape trials. Since then deep diving with free ascents has become an extreme sport and I think the record is around 1000 ft.

The WW2 escapes from 400 feet resulted in about 50% fatality rates from bends with additional deaths from exposure as the crews remained alone on the surface before rescue.

A modern escape from 750 feet is "exciting" in prospect. Five men in trunk, flood down then start pressurizing with 700 psi air. For survival the time from beginning pressurization until last man was out of the hatch had to be 15 seconds. Needless to say the pressurization would burst eardrums.

(The rest of the discussion is HERE.)

"Back in ancient days (before the fire burnt the water filled escape tower in '68) all submariners made qualification escapes from a 100 ft tank of water that was the tallest structure in the New London area (which was the reason the fire trucks could not stop the HP air/ hydraulics fire). Two types of escape -- a free escape with only a lifejacket, and the lifejacket plus Stenke Hood (a transparent plastic bag over the head with an air bubble - so you breathed (out obviously) into a "normal" environment instead of venting directly into water)"

Yup. I made that 'dive' back in '61 during submarine school there.