Editor's note: The Duramax engine's basic OHV layout with four valves per-cylinder has remained unchanged since 2001. An earlier version of this story contained an inaccurate description of the engine ...

Apart from the United States, more than 60 foreign militaries operate some 250,000 Humvees. (NATO) The most common vehicle operated by the U.S. military is the High Mobility Multipurpose Wheeled ...