The M113 is a fully tracked armored personnel carrier currently manufactured by BAE Systems. The vehicle was first fielded by United States Army's mechanized infantry units in Vietnam in April 1962. The M113 was the most widely used armored vehicle of the U.S. Army in the Vietnam War, earning the nickname 'Green Dragon' by the Viet Cong as it was used to break through heavy thickets in the midst of the jungle to attack and overrun enemy positions, but largely known as an APC and ACAV (armored cavalry assault vehicle) by the allied forces.
The M113 introduced new aluminum armor that made the vehicle much lighter than earlier vehicles; it was thick enough to protect the crew and passengers against small arms fire but light enough that the vehicle was air transportable and moderately amphibious. In the U.S. Army, the M113 series have long been replaced as front-line combat vehicles by the M2 and M3 Bradley, but large numbers are still used in support roles such as armored ambulance, mortar carrier, engineer vehicle, command vehicle, etc. The Army's Heavy Brigade Combat Teams are currently equipped with around 6,000 M113s and 4,000 Bradleys.
The M113's versatility spawned a wide variety of adaptations that live on worldwide, and in U.S. service. These variants together represent about half of U.S. Army armored vehicles today. To date, it is estimated that over 80,000 M113s of all types have been produced and used by over 50 countries worldwide, making it one of the most widely used armored fighting vehicles of all time. The Military Channel's "Top Ten" series named the M113 the most significant infantry vehicle in history. The U.S. Army planned to retire the M113 family of vehicles by 2018, seeking replacement with the GCV Infantry Fighting Vehicle program, but now replacement of the M113 has fallen to the Armored Multi-Purpose Vehicle (AMPV) program.
The M113 was developed by Food Machinery Corp. (FMC), which had produced the earlier M59 and M75 Armored personnel carriers. The M113 bore a very strong resemblance to both of these earlier vehicles. The M75 was too heavy and expensive to be useful; its weight prevented amphibious capability, and being transported by air. The lightened M59 addressed both of these problems, but ended up with too little armor, and was unreliable as a result of efforts to reduce its cost.
The Army was looking for a vehicle that combined the best features of both designs, the "Airborne Armored Multi-Purpose Vehicle Family" (AAM-PVF). of all-purpose, all-terrain armored fighting vehicles FMC had been working with Kaiser Aluminum and Chemical Co. in the late 1950s to develop a suitable aluminum armor. Use of this armor could produce a vehicle that provided the protection of the M75, and the light weight and mobility of the M59.
FMC responded with two proposals; two versions of the aluminum T113 - a thicker and a thinner armored one - along with the similar but mostly steel T117. The thicker-armored version of the T113, effectively the prototype of the M113, was chosen because it weighed less than the steel competitor, while offering the same level of protection. An improved T113 design, the T113E1, was adopted by the U.S. Army in 1960 as the M113. A diesel prototype T113E2 was put into production in 1964 as the M113A1, and quickly supplanted the gasoline-engined M113. In 1994, FMC transferred the M113's production over to its newly formed defense subsidiary, United Defense. Then in 2005, United Defense was acquired by BAE Systems.
U.S. Army soldiers dismount from an M113 armored personnel carrier during a training exercise in September 1985.
The M113 was developed to provide a survivable and reliable light tracked vehicle able to be air-lifted and air-dropped, by C-130 and C-141 transport planes. The original concept was that the vehicle would be used solely for transportation, bringing the troops forward under armor and then having them dismount for combat; the M113 would then retreat to the rear. Entering service with the U.S. Army in 1960, the M113 required only two crewmen, a driver and a commander, and carried 11 passengers inside the vehicle. Its main armament was a single .50-caliber (12.7 mm) M2 Browning machine gun operated by the commander.
On 30 March 1962, the first batch of 32 M113s arrived in Vietnam, and were sent to two Army of the Republic of Vietnam (ARVN) mechanized rifle companies, each equipped with 15 of the APCs (M113s). On 11 June 1962, the two mechanized units were fielded for the first time. During the Battle of Ap Bac in January 1963, at least fourteen of the exposed .50 caliber gunners aboard the M113s were killed in action, necessitating modifications to improve crew survivability. Soon, makeshift shields formed from metal salvaged from the hull(s) of sunken ships were fitted to the carriers, which afforded better protection. But, finding that this material could be penetrated by small arms fire, subsequent shields were constructed from scrapped armored vehicles.
The ARVN 80th Ordnance Unit in South Vietnam developed the shield idea further and commenced engineering general issue gun shields for the M113. These shields became the predecessor to the standardized Armored Cavalry Assault Vehicle (or ACAV) variant and were issued to all ARVN mechanized units during the early 1960s. The ARVNs had modified the M113s to function as "amphibious light tanks" and not as battle taxis as US designers had intended. Instead of an armored personnel carrier, the ARVN used the carried infantry as extra "dismountable soldiers" in "an over-sized tank crew." These "ACAV" sets were eventually adapted to U.S. Army M113s with the arrival of the Army's conventional forces in 1965. The vehicles continued to operate in the role of a light tank and reconnaissance vehicle, and did not operate as designed in theater. Still, the M113 could carry 11 infantrymen inside, with two crewmen operating the M113.