U.S. Army 2nd Staff and Faculty Company Watercraft Engineer Certification Course students rebuild Detroit diesel 12-V-71 series main propulsion engines at Fort Eustis, Va., May 21, 2015. While working on engines like the 12-V-71, students must use precise measures when maintaining or repairing any part. (U.S. Air Force photo by Staff Sgt. Natasha Stannard/Released)