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Using M113 APCs as Tanks? The Vietnam Story

New video on South Vietnam's (ARVN) Armored Cavalry during the Vietnam War, with a focus on their M113 ACAV units that employed modified M113 APCs like tank tanks. The American 11th ACR did something similar, having been influenced by ARVN SOPs before their deployment.

↓ ARVN Tables of Organization

The following are the original Tables of Organization for the ARVN Armored Cavalry Squadron (H&S Troop, Armored Cavalry Assault Troop, and M41 Tank Troop) from 1968.

Download PDF • 7.03MB
ARVN ARCAV Assault Trp
Download PDF • 2.52MB
ARVN M41 Tank Trp
Download PDF • 3.44MB

↓ Accompanying Graphics

↓ Script

[I’ve posted 7 new articles on my website since my last video, and I’ve also uploaded the original ARVN tables of organization this video is based on. Create a free account on to get email notifications when I upload new articles, videos, and primary source documents.

The M113 is a tracked armored personnel carrier adopted by the US in the early 1960s. It served as the primary transportation for their mechanized infantry until it was phased out of this role by the Bradley fighting vehicle.

Most mil nerds will know that the M113 isn’t a tank. It was designed as a battle taxi that drops off infantry, maybe a terrain-feature away, and either hides or takes up hull-down support by fire positions to cover the dismounted attack.

However, in Vietnam, some units fought M113s as tank units, with tank platoon structures, no dismounts, and a tank-like mission.

There is a conventional wisdom of what a tank is. The Conventional Armed Forces in Europe Treaty defines the battle tank as a self-propelled armored fighting vehicle that weighs at least 16.5 metric tonnes, with a direct-fire high velocity cannon at least 75mm in caliber which can be traversed 360 degrees, a high degree of cross-country mobility and protection, and which is not primarily designed to carry infantry. This vehicle can either be tracked or wheeled provided it meets the other criteria.

But aside from technical definitions which can get you bogged down in semantics hell, there is the distinct concept of a tank-like role that I find interesting.

Specifications are absolutes, mostly. The road speed of a tank is an absolute figure. The size and mass of a tank’s sabot round are absolute figures. But combat isn’t about absolutes. Capability is framed in reference to the enemy. If the enemy has no anti-tank weapons, Abrams-level protection probably isn’t required to bring about similar effects. If the enemy is footmobile, any amount of motorized mobility could be advantageous. And if the enemy’s tanks aren’t well-protected by modern standards or they have no tanks at all, firepower can be reduced in favor of other things, like higher ammo capacity, lower weight or higher rate of fire.

Against an enemy like the US faced in Europe during World War II, a Stuart light tank is probably going to be relegated to its doctrinal role of reconnaissance support and security. But in the Pacific, that same light tank could credibly fill a role equivalent to a main tank because of Japan’s lesser armor and anti-armor capabilities. And for similar reasons the French can deploy AMX-10RCs or ERC-90s to Africa and have them fill a tank-like role while retaining the advantages wheels and lighter weight provide. But while peacekeeping in Lebanon, where the deterred party has main battle tanks, they deploy Leclerc MBTs. It’s relational to the enemy.

At its most extreme, this dynamic applied to the M113 during the Vietnam War.

The center-piece was the Armored Cavalry Assault Vehicle, which despite still being an aluminum box, is often lauded as one of the most effective armored vehicles of the war.

The predecessor to the ACAV was developed by the South Vietnamese in the early 1960s before the US ever started major ground combat operations. In April of 1962, the US provided the Vietnamese with two M113 companies assigned to their 7th and 21st Infantry Divisions.

These companies were initially based on US Mechanized Infantry Companies, with an HQ, 3 rifle platoons, and a support platoon with 60mm mortars and bazookas. U.S. advisers initially wanted the Vietnamese to use the M113 like the Americans. Maneuver around the enemy’s flank and dismount their infantry for the actual attack. But ARVN charged the enemy straight up through flooded terrain, scattering the guerrillas with shock effect, and quickly gaining fire superiority with their .50 cals. When their troops did dismount at the request of American advisers, the inexperienced infantry would get bogged down in marshy terrain, and all of the sudden, the Vietcong’s small arms became effective.

It quickly became SOP for M113 troops to fight mounted, and American advisers passed this knowledge onto the US Armored Cavalry Regiments, who would replace many of their jeeps, tanks and M114s with ACAVs for their own deployments.

Mounted troops generally suffered fewer casualties than the dismounted. Although protection and armament was obviously inferior to an MBT, the M113 did have the advantage of being amphibious. So they still maintained a huge mobility advantage over both the VC and tanks as well when operating in inundated terrain that characterized the country’s far south.

The French also learned this lesson during the First Indochina War in the 1950s, and implemented amphibious cavalry squadrons manned mainly by Vietnamese troops. See the article I wrote on that topic in the pinned comment.

Even in jungle warfare, which is famously infantry centric, M113s played a decent jungle-busting role, driving ahead of the infantry to detonate anti-personnel mines, break through the bush, and break up enemy ambushes. However, the M41 Walker Bulldog was better at this, and the M48 Patton even more so.

The more direct role of the ACAVs was reflected in its modifications. From 1963, ARVN’s 2nd Armored Cavalry and 80th Ordnance Depot began fabricating gunshields for their .50 cals, after they lost 14 track commanders manning the unprotected MG. When the US 11th Armored Cavalry Regiment standardized the ACAV in 1966, they added two sidemounts for medium MGs. The US and South Koreans used M60s. But ARVN had M1919A4s chambered in .30-06 in their organization tables. ACAVs also had hatch armor and an improved turret shield to provide 360 degree protection for the .50 gunner. Notably, US versions of the M113 used diesel engines, while Vietnamese versions ran on gasoline, which increased the ARVN version’s susceptibility to serious casualties during mine strikes.

The Viet Cong and North Vietnamese eventually adapted to this state of affairs, as they received anti-armor weapons in the form of recoilless rifles, mines, armor piercing MG ammo, and RPG-2s. ARVN would replace their old French Chaffees with newer Walker Bulldogs in 1964, and with North Vietnam bringing T-54s and PT-76s to the fight by the early 70s, they received M48 Pattons as well. But for a brief time, the VC had no answer to South Vietnamese APCs, and M113s made up the bulk of ARVN cavalry to the end.

As well as survivability modifications, changes came to the unit organizations. Mechanized rifle companies were initially redesignated as mechanized rifle squadrons in 1962, as they became the 4th and 5th squadrons of the 2nd Armored Cavalry Regiment.

But they only received minor org changes, with the replacement of 60mm mortars and bazookas with dismounted M1 81mm mortars and M18 57mm recoilless rifles.

But around 1967, there were even bigger changes. Mechanized Rifle Squadrons were redesignated as Armor Cavalry Assault Troops.

The troop’s subordinate platoons were reorganized like tank platoons. Instead of 3 APCs and 3 rifle squads, they had 5 ACAVs with only enough men to man the track and all its weaponry.

Infantry missions were not the priority, although there is footage of heavily manned ARVN ACAVs dismounting extra infantry. They were “To close with and destroy enemy forces, using fire, maneuver and shock action in coordination with other combat units, particularly on terrain improper for tanks.” This is basically word-for-word the same mission as US Tank Companies of the time.

Each track had a 7-man crew, including the track commander who depending on the vehicle was just a commander, or platoon leader, assistant platoon leader or section leader. Each had a driver, .50 cal gunner, two .30 cal gunners, an M79 grenadier, and an ammunition bearer.

Two tracks made up an assault section, under either an E8 Section Leader or Assistant Platoon Leader who was a junior officer. Two assault sections made up the bulk of the platoon, while the HQ had the Lieutenant Platoon Leader, his ACAV, and an identical crew.

Assault Troops had 3 of these platoons, in addition to a support platoon and HQ platoon.

Support platoon had an HQ, a mortar section with 3 M125 81mm mortar carriers, and a recoilless rifle and assault bridging section with 2 recoilless rifles and 1 lightweight assault bridge that could be mounted on an ACAV. In the 1968 TO&E the recoilless rifles are listed as the same 57mm, but by 1970 at least they were using M40 106mms. This gave the troop decent direct-fire capabilities beyond their .50 cals.

The HQ had an HQ Section, Maintenance Section, and Admin and Supply Section. With a total of 19 M113s per troop. By a 1970 report, it’s noted that one of the HQ ACAVs was replaced by an M577 command vehicle.

The troop overall, while templated for a Major, was typically commanded by a 1st Lieutenant in practice. He was assisted by an American adviser team, consisting of a Captain and a Senior NCO, normally a Sergeant First Class.

The next level up was the Armored Cavalry Squadron, which had evolved significantly since the French days. Back in 1963, they were regiments, with one company sized squadron each of M24 Chaffee light tanks, M8 armored cars, and M114 recon vehicles, plus two mechanized rifle squadrons on M113s.

By 1970, they were battalion-sized squadrons and had two variants. One with 3 Armored Cavalry Assault Troops, and one with two ACATs and one tank troop with 17 M41 Walker Bulldog light tanks. Three platoons with 5 tanks each plus 2 HQ tanks. The M41 had been phased out of US cavalry organizations in favor of the M48 Patton back in the late 1950s, but it was a satisfactory replacement for the busted M24s the French left ARVN.

Both variants had a Headquarters and Service Company, templated for a Colonel commanding but more often with a Lieutenant Colonel or Major at the helm, plus an American Major leading an advising team. If the squadron had a tank troop, it’d also have 2 M41s in the HQ.

Other armor included a flamethrower section with 2 M132 armored flamethrowers, and a recon platoon with 6 V-100 Commando armored cars. Although it’s noted that these Commandos were mainly used for convoy security and typically didn’t work directly for the squadron.

With the 1968 Vietnamese Armed Forces Expansion Program, armored cav command structures were shifted. Under the old model, each of the 10 infantry divisions had an armored cavalry squadron. But with the new model, they’d be grouped into four armored cavalry brigades. One per Corps Tactical Zone or military region. Although about half of the squadrons would maintain relationships with individual infantry divisions. This was intended to give the corps an armored rapid reaction unit with armor commanders at the helm.

By the end of the conflict, 1st and 2nd Brigades had 4 each of the combo M113 /M41 squadrons, while 3rd Brigade had 5. 4th Brigade, which supported the corps overseeing the Mekong Delta region, covered in swamps, flooded rice paddies, and other water features had 5 of the M113-only variant due to its superior performance in this type of terrain.

Beginning in 1971, the US also began supplying ARVN with M48A3 Pattons, the first being the 20th Squadron under the 1st Brigade directly on the border with North Vietnam, followed by the 22nd under the 3rd Brigade near Saigon, and finally the 21st under the 2nd Brigade at Pleiku.

After the fall of the south, much of this equipment transferred to the People’s Army of Vietnam, and the M113 is still in active Vietnamese service today.

If you’d like more info on the Cold War application of the M113, check out this video on the US Mechanized Infantry squad evolution in the 1980s. We’ll see you over there.]

↓ Sources

[1] Graphic derived from FM 7-7 "The Mechanized Infantry Platoon and Squad (APC)" (March 1985)

[2] Conventional Armed Forces in Europe Treaty (CFE Treaty) (1990)

[3] FM 2-30 "Cavalry Mechanized Reconnaissance Squadron" (March 1943)

[4] FM 17-32 "The Tank Company, Light and Medium" (Aug 1942)

[5] "Tactical Documentary Base for the Use of Staff School Trainees" (2017)

[6] Starry, D (2002) "Mounted Combat in Vietnam"

[7] Kerns, B (2006) "Not Just an Infantryman's War: United States Armored Cavalry of the Vietnam War"

[8] TOE TG-135 "Mechanized Rifle Troop" (15 June 1963)

[9] TO&E 8-705A "Armor Cavalry Assault Troop" (1968)

[10] Robinson, D (FY70) "Armored Cavalry Squadron" referring to period from 1968 to 1969

[11] TO&E 8-703A "Tank Troop" (1968)

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