Students participating in a Survive, Evade, Resist, Escape refresher course climb into a 12-man life raft during simulated rough water exercise Nov. 17, 2011 at the Prince George's Sports & Learning Complex in Landover, Md. Air crews must attend a S.E.R.E. refresher course every three years to keep up to date on their training and learn new S.E.R.E. tactics.