FILE - In this May 16, 2012, file photo, released by the U.S. Navy, Petty Officer 3rd Class DonPaul Mitchell, left, assigned to the guided-missile submarine USS Georgia, instructs Ensign Tabitha Strobel, Georgia's main propulsion assistant, in a trainer at Naval Submarine Base Kings Bay in Georgia. With women now serving on submarines, future subs are being built to specifically accommodate gender differences including height, reach and strength. The first vessel built with some of the new features is expected to be delivered in 2021. (James Kimber/U.S. Navy via AP, File)