Back in the day, you weighted yourself to be neutral at your operating depth and kicked hard to get down. In cold water, this was a reasonable effort. At the end of a dive you simply rose back to the surface - no three-minute safety stop.
A scabillion years ago when I was learning to dive in cold water, you could always tell if a dive site was popular by the little piles of rocks or lead that would get ditched at 15 - 30 feet after the 1/2" foam suits collapsed. Pretty regularly people would miss them on the way back out...