Many years ago, I attended a marine college to qualify for working on ships. Besides an intense academic curriculum, they also were keen on getting us physically fit for life at sea.
Every weekday morning before breakfast we had swim training in the pool, which I really enjoyed. We were told to always swim in seaman's rain suits which felt good and comfortable in the water, but were hard to swim in.
Three times a week we practiced various aspects of sea survival and safety training in the pool. This was good fun, but tough. We had to wear the usual rain suits on top of two layers of clothing, plus boots. Practice included life rafts, clothes inflation for buoyancy, jumping from heights, and swimming underwater.
Most of us now work for the ferry company, so we come home every day and meet for swim training.