The M113 series of armored personnel carriers was developed by FMC Corporation (now United Defense) for the US Army, and has become one of the most widely used military vehicles in the world today. Since production commenced in 1960, more than 75,000 M113 series vehicles have been built, serving in the armed forces of some 41 nations in 20 different known versions. The origin of the M113 dates back to a 1954 requirement for a family of airportable tracked vehicles to replace the existing M59 and M75 APCs. A prototype was constructed in 1958, and production of M113s (originally with a petrol engine) commenced in 1960 at the FMC plant at San Jose, California. In the same year work was begun to substitute a 215 bhp GMC 6-cyl diesel engine, and production of this version, the M113A1 (commenced in 1963), would soon become the production standard from then on. In addition to the US built M113s production has also been undertaken at OTO-Melara, Italy for delivery to the Italian and Greek Armed Forces.
Combat experience during the Vietnam War soon disclosed the fact that the light armor on the M113 was barely able to stop a non-armor piercing rifle bullet and many casualties were caused to crew and passengers when the vehicle was struck by shaped explosive charges or missile warheads. Consequently later versions would receive additional bolt-on aluminum armor panels and interior Kevlar liners for the protection of the passengers. The price paid to make the M113 fully amphibious was the revolutionary high sided hull of welded aluminum which although allowing the vehicle to float with about one foot of freeboard when fully loaded also made the M113 vulnerable on the battlefield. Speed afloat is extremely slow, the M113 being propelled through the water by its tracks alone at just 3.6 mph.
Despite these drawbacks the M113 has formed the basis of many specialized vehicles, including various Mortar carriers, command vehicles, missile carriers, recovery vehicles and self propelled anti-aircraft systems, among many other innovations. Later models of the APC (M113A2 and M113A3) would include a number of modifications including full NBC protection, Passive night vision equipment, and a more powerful 275 bhp Detroit Diesel 6V-53T diesel engine. Whilst no longer having the speed to keep up with the latest M1 Abrams tanks on the modern battlefield, the M113 in its many variants is still expected to provide useful service for many years to come
