The M113 is an armored personnel carrier of US origin. It was developed in the late 1950's as a replacement for the M75 and M59 armored personnel carriers. The M75 was well armored and expensive while the M59 was highly mobile but lack protection and reliability. The M113 is one of the most numerous combat vehicles ever produced and served as a chassis for a wide variety specialist versions, some of which are described in an article of their own.

The M113 has the same layout as the earlier M75 and M59 in being an armored box on a tracked chassis. The engine and driver are located at the front. The troop compartment is located at the rear and is accessed trough a large ramp at the rear. The commander is seated behind the engine in the middle and has access to a low profile cupola which usually mounts a 12.7mm M2HB heavy machine gun.

The M113 is armed with a 12.7mm M2HB heavy machine gun on a ring mount that is usually fitted with a gun shield and all round armored plates. The Vietnam era ACAV modification added a 7.62mm M60 machine gun behind a gun shield on each side. The M113 chassis has been used for many weapon platforms such as tank destroyers with the 106mm M40 recoilless rifles or TOW missiles and mortar carriers with a 81mm, 107mm or 120mm mortar.

The M113 has aluminum armor that protects against small arms fire and shell splinters all around. Several improvement kits exist to increase protection against larger caliber rounds and slat armor can be fitted to reduce the effect of anti-tank missiles. An NBC system is standard and smoke grenade dischargers are optional.

The tracked chassis gives the M113 a very good cross country mobility. Originally a 209 hp petrol engine was fitted, but this was changed to a diesel engine in all subsequent production models. The maximum of 68 km/h is adequate but does not allow it to keep up with the M1 Abrams and M2 Bradley. The M113 is fully amphibious and propels itself in the water using its tracks.

The main operator of the M113 was the US army, but many have been exported to US allies with most being NATO members. With the introduction of the better armed and armored M2 Bradley and the faster Stryker the use of the M113 in US service has been reduced significantly. Many US M113's have been exported as well. In foreign service M113's have often been upgraded with various armor kits and weapon stations not found in US service.