U.S. Army 2nd Staff and Faculty Watercraft Engineer Certification Course students rebuild Detroit diesel 12-V-71 series main propulsion engines according to technical manuals at Fort Eustis, Va., May 21, 2015. The engines are rebuilt according to the engine’s technical manual and safety notes to ensure no mechanical or safety mishaps occur. (U.S. Air Force photo by Staff Sgt. Natasha Stannard/Released)