The M113 was first used in combat in April 1962 after the United States provided the South Vietnamese army (ARVN) with heavy weaponry such as the M113, under the Military Assistance Command, Vietnam (MACV) program.

Eventually, the M113 was the most widely used armored vehicle of the U.S. Army in the Vietnam War and was used to break through heavy thickets in the midst of the jungle to attack and overrun enemy positions.

[7] Thousands of M113s continue to see combat service in the Israel Defense Forces, although by 2014 the IDF was seeking to gradually replace many of its 6,000 M113s with the Namers,[8] and with the Eitan AFV in 2020.

The original concept was that the vehicle would be used solely for transportation to move the troops forward under the protection of armor and then having them dismount for combat, after which the M113 would retreat to the rear.

[13] During the Battle of Ap Bac in January 1963, at least fourteen of the gunners aboard the M113s were killed in action due to their exposed position, necessitating modifications to improve crew survivability.

[15] 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.

[16] Instead of an armored personnel carrier, the ARVN used the carried infantry as extra "dismountable soldiers" in "an oversized tank crew".

This more or less standardized ACAV kit included shields and a circular turret for the .50-caliber M2 machine gun in the track commander (TC) position, two M60 machine guns with shields for the left and right rear positions, and "belly armor"—steel armor bolted from the front bottom extending 1/2 to 2/3 of the way towards the bottom rear of the M113.

Although neither the XM701 or XM734 were deemed worthwhile to produce, FMC continued development of their version as the XM765 advanced infantry fighting vehicle (AIFV).

The German Army has various nicknames, depending on location and branch of service, including "elephant shoe",[21] "Tank Wedge"[22] and "bathtub".

Original production M113s can swim without deploying flotation curtains, using only a front-mounted trim vane; they are propelled in the water by their tracks.

During the Vietnam War, U.S. Army gun trucks, along with V-100 armored cars, conducted convoy escorts for military traffic.

[29][30] Additional M113s were supplied to the Cambodian Khmer National Armed Forces, equipped with a turret for the machine gun and a M40 recoilless rifle mounted on the roof.

The MRV featured a Scorpion turret with 76 mm gun, improved fire control, and passive night vision equipment.

PLO ambushes with RPGs caused extensive casualties because of the tendency of the M113's aluminum armor to catch on fire after being hit by anti-tank weapons.

The vulnerability of the M113 armored personnel carrier to IEDs and RPGs led the IDF to later begin to develop the Namer APC.

As a result, the IDF faced calls from the Israeli public to build more Namer APCs over the next decade and to gradually reduce the number of M113s used in its future combat operations.

[36] On 24 June 2024, Al-Qassam Brigades published footage of its forces attacking an M113 using a Chinese HJ-8 ATGM, hitting the vehicle, caused an external fire on the carry-on CARPET demining system.

[37] Several disabled Zelda APCs in Nabatieh, Lebanon and Gaza have revealed VBIED use by the IDF, where the vehicles are filled with explosives, towed to their target, and detonated.

On numerous occasions since their introduction in the late 1960s, the IDF's M113s have proven vulnerable to modern anti-tank missiles, IEDs, and RPGs, resulting in the deaths of many Israeli soldiers riding inside the vehicles.

The IDF has nonetheless been unable to replace the use of them in combat operations, due to budget constraints in equipping its large mechanized infantry regiments.

Designed to serve alongside the tracked Namer, the Eitan is planned to be cheaper and lighter, at 35 tons, incorporating an active protection system and a turret.

An M113 belonging to the Midland County Sheriff's Department was used in the 2008 raid of the Fundamentalist Church of Jesus Christ of Latter Day Saints compound.

[45] The Brazilian Marine Corps's M113s were used in joint operations with Batalhão de Operações Policiais Especiais during the 2010 raid on Complexo do Alemão.

This included a yoke for steering instead of laterals, a brake pedal, a more powerful engine (the turbocharged 6V-53T Detroit Diesel),[57] and internal spall liners for improved protection.

Armored fuel tanks were added externally on both sides of the rear ramp, freeing up 0.45 cubic metres (16 cu ft) of internal space.

A huge number of vehicles based on the running gear of the M113 have been created, ranging from APCs to tactical ballistic missile launchers.

Self-propelled variant of the M167 VADS short-range air-defense system, mounting an M61 Vulcan cannon with a radar rangefinder and 2,100 rounds of ammunition on a modified M113 chassis (M741 carrier).

Its hull is lengthened by 34 inches and equipped with an additional road wheel (six on each side) to sustain the added dry weight and payload.

Egypt produces many variants of the M113 including the Egyptian Infantry Fighting Vehicle (EIFV), which features a combination of an M113A3-base and the fully functional and stabilized two-man turret of the M2 Bradley.