I recently completed a Marine STCW Class and Two instructors, one EMT-PM and a USCG Ret. Capt of S& R commented slow reheat is best. Warm bodies work best, no hot liquids, be gentle as body at that point is fragile. Dry clothes, cover head, cover top and bottom with blankets. Too fast of reheat "fools" body and allows cold blood to reenter heart causing failures. Too warm can cause burns. Most Hypothermic patients do not realize it can only take a few seconds in 50 degree or less water.