Armored Personnel Carriers with troops of the 11th Armored Cavalry Regiment aboard grind their way through underbrush in Tay Ninh Province, about a mile and a half away from the Cambodian border on March 18, 1970, as they proceed towards an enemy base camp. The troops were checking the area to determine effectiveness of a recent B-52 bomber strike on the base camp. (AP Photo/Charles Ryan)

Photo of 11th Armored Cavalry "Blackhorse" Regiment patchThe 11th Armored Cavalry “Blackhorse” Regiment traces its origins to the 11th Cavalry Regiment, formed in 1901. After a series of redesignatons, it became the 11th Armored Cavalry Regiment in 1948. The unit served in Vietnam 1966-72. (Historynet Archives)

One of the U.S. Army’s specialized units in Vietnam was the 11th Armored Cavalry Regiment, nicknamed the “Blackhorse Regiment.” When deployed in 1966, the regiment was equipped primarily with M113 armored personnel carriers modified with additional guns and shields to become “armored cavalry assault vehicles” for a more offensive role. The ACAV’s basic armament consisted of two 7.62 mm M60 machines guns mounted on either side of the cargo top hatch and a .50-caliber M2 machine gun upfront, protected by a rounded armored collar with armor plates fore and aft to afford more protection for the gunner. Backed by flamethrower-equipped M113s called M132 “Zippos,” M551 Sheridan light tanks and M109 self-propelled howitzers, Blackhorse ACAV crews fought with distinctive aggressiveness in numerous operations in the Saigon area between 1966 and 1972. By mid-1967 mechanized infantry units, which also used M113s, were retrofitting their vehicles to make them similar to ACAVs, but their tactics still differed. Mechanized infantry fought both mounted and dismounted, while the armored cavalry primarily operated mounted and on the move. The Blackhorse Regiment, with three squadrons, was the only full armored cavalry regiment in Vietnam, but most infantry divisions had their own armored cavalry squadrons, adding five to the list: 1st Squadron, 4th Cavalry Regiment, 1st Infantry Division; 1st Squadron, 10th Cavalry, 4th Division; 3rd Squadron, 5th Cavalry, 9th Division; 1st Squadron, 1st Cavalry, 23rd Division (Americal); and 3rd Squadron, 4th Cavalry, 25th Division.

This article appeared in the Autumn 2022 issue of Vietnam magazine.

American troopers from the U.S. 11th Armored Cavalry have been clearing parts of the woods, known as the Ho Bo woods, 25 miles northwest of Saigon on May 27, 1971. (AP Photo/Rick Merron) Sending a handwritten message to the enemy are troops from the 11th Armored Cavalry clearing the Bo Ho Woods area northwest of Saigon on May 27, 1971. (AP Photo/Rick Merron)

Soldiers in Troop E, 1st Squadron, 1st Cavalry Regiment, 23rd Infantry Division (Americal), halt for awhile.Soldiers in Troop E, 1st Squadron, 1st Cavalry Regiment, 23rd Infantry Division (Americal), halt for awhile. (Jerzy Krzeminski)

Soldiers of the U.S. 11th Armored Cavalry Regiment are silhouetted atop their tank by the glare of tracer bullets in Cambodia, July 6, 1970. In an exercise known as Mad Minute, they spray the area around them, possibly infiltrated by enemy patrols, before they move on. (AP Photo/Henri Huet)M113 crewmen of the 11th Armored Cav in Cambodia on the night of July 6, 1970, are silhouetted in the glare of tracer bullets during a “mad minute” exercise, in which they spray the area around them to detect enemy infiltration before moving on. (AP Photo/Henri Huet)

A member of Troop L, 3rd Squadron, 11th Armored Cav guides an ACAV across a river ford during Operation Junction City Phase II north of Saigon on April 7, 1967.A member of Troop L, 3rd Squadron, 11th Armored Cav guides an ACAV across a river ford during Operation Junction City Phase II north of Saigon on April 7, 1967. (National archives)

US soldiers of 1st Squadron, 4th Cavalry on Zippo Tracks armored personnel carriers incinerating Iron Triangle area during Operation Cedar Falls. (Photo by Dick Swanson/Getty Images)An M132 “Zippo” armored flamethrower of 1st Squadron, 4th Cavalry Regiment, 1st Infantry Division, incinerates an enemy position in the Iron Triangle between Saigon and Cambodia during Operation Cedar Falls in January 1967. (Photo by Dick Swanson/Getty Images)

An ACAV crewman from the 11th Armored Cavalry works outside the vehicle.An ACAV crewman from the 11th Armored Cavalry works outside the vehicle. (Joseph Gibbs Collection)

An armored personnel carrier of 2nd squad, 11th armored cavalry plows through monsoon mud at firebase warrior 25 miles northwest of Saigon in Vietnam on Sept. 18, 1971. The cavalry conducts defensive operations and monitors enemy infiltration routes from Cambodia to Saigon. (AP Photo)Soldiers of the 11th Armored Cavalry’s 2nd Squadron slog through monsoon mud near Fire Support Base Warrior 25 miles northwest of Saigon on Sept. 18, 1971. (AP Photo)

M113 ACAVs and M551 Sheridan tanks of 1st Squadron, 1st Cavalry, attached to the 23rd Infantry Division (Americal), prepare for an operation in August 1968.M113 ACAVs and M551 Sheridan tanks of 1st Squadron, 1st Cavalry, attached to the 23rd Infantry Division (Americal), prepare for an operation in August 1968. (Jerzy Krzeminski/John Krisman collection)

Armored cavalry assault vehicles move in file across a swampy jungle clearing in war Zone C, some 20 miles north of Tay Ninh on Feb. 24, 1967. The tracks of other tanks and armored vehicles are already imprinted into the high swamp grass, while infantrymen ring and seal off C zone in a horseshoe like deployment the armor pushes right into the heart of C zone from the south. (AP Photo/Kim Ki Sam)ACAVs move in file across a clearing in War Zone C, along the Cambodian border, on Feb. 24, 1967. The tracks of other armored vehicles are already imprinted into ground. (AP Photo/Kim Ki Sam)

Armored Personnel Carriers with troops of the 11th Armored Cavalry Regiment aboard grind their way through underbrush in Tay Ninh Province, about a mile and a half away from the Cambodian border on March 18, 1970, as they proceed towards an enemy base camp. The troops were checking the area to determine effectiveness of a recent B-52 bomber strike on the base camp. (AP Photo/Charles Ryan)M113 armored cavalry assault vehicles, or ACAVs, and M551 Sheridan light tanks of the 11th Armored Cavalry Regiment plow through rough terrain about a mile and a half from the Cambodian border on March 18, 1970. (AP Photo/Charles Ryan)

American troopers from the U.S. 11th Armored Cavalry have been clearing parts of the woods, known as the Ho Bo woods, 25 miles northwest of Saigon on May 27, 1971. (AP Photo/Rick Merron)Soldiers in Troop E, 1st Squadron, 1st Cavalry Regiment, 23rd Infantry Division (Americal), halt for awhile.Soldiers of the U.S. 11th Armored Cavalry Regiment are silhouetted atop their tank by the glare of tracer bullets in Cambodia, July 6, 1970. In an exercise known as Mad Minute, they spray the area around them, possibly infiltrated by enemy patrols, before they move on. (AP Photo/Henri Huet)A member of Troop L, 3rd Squadron, 11th Armored Cav guides an ACAV across a river ford during Operation Junction City Phase II north of Saigon on April 7, 1967.US soldiers of 1st Squadron, 4th Cavalry on Zippo Tracks armored personnel carriers incinerating Iron Triangle area during Operation Cedar Falls. (Photo by Dick Swanson/Getty Images)An ACAV crewman from the 11th Armored Cavalry works outside the vehicle.An armored personnel carrier of 2nd squad, 11th armored cavalry plows through monsoon mud at firebase warrior 25 miles northwest of Saigon in Vietnam on Sept. 18, 1971. The cavalry conducts defensive operations and monitors enemy infiltration routes from Cambodia to Saigon. (AP Photo)M113 ACAVs and M551 Sheridan tanks of 1st Squadron, 1st Cavalry, attached to the 23rd Infantry Division (Americal), prepare for an operation in August 1968.Armored cavalry assault vehicles move in file across a swampy jungle clearing in war Zone C, some 20 miles north of Tay Ninh on Feb. 24, 1967. The tracks of other tanks and armored vehicles are already imprinted into the high swamp grass, while infantrymen ring and seal off C zone in a horseshoe like deployment the armor pushes right into the heart of C zone from the south. (AP Photo/Kim Ki Sam)Armored Personnel Carriers with troops of the 11th Armored Cavalry Regiment aboard grind their way through underbrush in Tay Ninh Province, about a mile and a half away from the Cambodian border on March 18, 1970, as they proceed towards an enemy base camp. The troops were checking the area to determine effectiveness of a recent B-52 bomber strike on the base camp. (AP Photo/Charles Ryan)

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