The M-113 armored personnel carrier, though not a tank, was adapted with many types of weapons and upgraded with steel plating for aggressive use. It usually has a 3 man crew and can carry 11 fully loaded and equipped troops into combat, with the troops exiting the rear by a hydraulically operated ramp system for extra protection. It is amphibious, using its tracks for propulsion. First produced in the early 1960s by the FMC Manufacturing Company, it used a Chrysler 75M-V8 engine with an Allison TX-200-2 conversion unit to propel the tracks, and later models were modified to use diesel fuel because it was safer. Many thousands were produced, and although the Bradley Fighting Vehicle and more recently the "Stryker" are being used, this vehicle remains in use around the world by U.S. forces and 50 other friendly nations.