070803-N-7981E-082 Pacific Ocean (August 3, 2007)- Aircrew Survival Equipmentman Airman William Halstead trains Aircrew Survival Equpmentman Airman Vanessa Hernandez to operate the Oxygen System Components Test Stand, known as the "Green Machine" inside the Aircraft Intermediate Maintenance Department (AIMD) Oxygen Shop aboard the Nimitz-class aircraft carrier USS Abraham Lincoln (CVN 72). The "Green Machine" is used to ensure oxygen system components used by aircrews perform properly at different altitudes by subjecting them to varying degrees of atmospheric pressure. Lincoln and embarked Carrier Air Wing (CVW) 2 are underway off the coast of Southern California conducting a Tailored Ship's Training Availability. U.S. Navy photo by Mass Communications Specialist 3rd Class James R. Evans (RELEASED)