First thing that happens when the cold water hits your groin is you stop breathing and you can go into cold water shock. We learned in Arctic training that no one can beat heat loss from your core in cold water. It's not something you can train your body to get better at. Once you're in the cold water you only have 10 minutes before you start to lose muscle control to hands, feet, arms, and the harder you fight the greater the loss of heat from your core. In 1 hour you develop hypothermia and die. Once that soldier is out of the water the first thing he must do is strip naked and jump into snow to dry off then wrap in a dry blanket and fresh fatigues. Keeping wet clothes on greatly increases heat loss versus cold dry air.