U.S. Air Force Airmen from the Special Tactics Training Squadron wait for the command to swim in the pool during water a confidence training evaluation, Hurlburt Field, Fla., Sept. 30, 2011. The evaluation tests the students? ability to hold their breath for extended periods of time while tying various knots on the bottom of the pool. (U.S. Air Force Photo/Airman Naomi M. Griego)(Released)