The M551 Sheridan Armored Reconnaissance/Airborne Assault Vehicle (AR/AAV) was a US light tank designed to be dropped by parachute, swim across rivers and was the last light tank employed by the US Army. It was armed with the technically advanced but problematic 152mm gun/launcher, which fired both conventional ammunition and the MGM-51 Shillelagh guided anti-tank missile. The Sheridan saw extensive combat in the Vietnam War where problems with the tank became evident, particularly its poor survivability and reliability. In 1979, the US Army began to eliminate the M551 from its inventory but a small fleet of M551s remained in service with the US 82nd Airborne Division and the National Guard. The Sheridan went on to serve in the 1989 invasion of Panama and 1990-91 Desert Shield/Storm.
During The Korean War (1950-53), the 76mm M41 Walker Bulldog light tank came into service with the US Army replacing the aging WWII vintage M24 Chaffee light tanks. It was a marked improvement over the M24 but it fell short of the then specifications for a light tank, notably its weight and short range, and thus was considered only an interim tank. In May 1952, specifications for the successor to the M41 were drawn up. By July 1953, proposals had been received from the Detroit Arsenal, Cadillac Motor Car Division of General Motors and Aircraft Armaments, Incorporated (AAI). The AAI design, the T92 gun tank armed with a 76mm gun, was selected for further development and the first pilot tank arrived at the Aberdeen Proving Grounds, Maryland, for testing on 2 November 1956. The T92 was a very compact vehicle with less volume to protect allowing the weight of the armor to be reduced which also had the further benefit of a being a small target. The T92 was much smaller than the M41. Despite a few bug corrections, testing went well and it was expected the T92 would begin full-scale production by mid-1962. However, in 1957, those plans had unexpectedly changed.
This is the second T92 pilot tank which arrived at Aberdeen on 22 July 1957. On both sides of the turret were two cupolas mounting machine guns which could rotate independently of the turret. Note the vision ports beneath the cupola and were on both sides. This T92 pilot was revised with a compensating-idler wheel and received the tracks from the M24 Chaffee.
A Congressional committee reviewing military matters noted that the Soviet Union had a light tank, the PT-76 armed with a 76.2mm gun, but it was amphibious and they questioned why our new light tank is not amphibious. This led to the change in the specifications for the US light tank to also be amphibious. The T92 currently under development was assessed to see if it could be made into an amphibious vehicle but it simply would not float and it could not reasonably be made to float.
In August 1957, the US Army completely changed their method of classifying tanks. For all future developments, it was mandated that the US will only have one type of tank, classified as the Main Battle Tank. There would be no more light, medium, heavy, 76mm, 90mm, 120mm, etc., tank designations. To augment the Main Battle Tank, there would also be the Armored Reconnaissance/Airborne Assault Vehicle (AR/AAV). Because of this classification change, the new AR/AAV would replace the T92. In June 1958, the T92 project was cancelled and the AAI engineers returned to their drawing boards to design a tank which met the current specifications and was also amphibious.
In July 1959, specifications for the Armored Reconnaissance/Airborne Assault Vehicle was presented to the US manufacturers and in October 1959 two of twelve responses were selected for further study. One design was submitted from AAI and the other from Cadillac. In 1960, Cadillac was awarded a contract to further develop their design which was designated the XM551. In August 1961, the Secretary of the Army approved the name for the first Armored Reconnaissance/Airborne Assault Vehicle.
The M551 was named in honor of General Philip Henry Sheridan (6 March 1831 to 5 August 1888), a US Union Army officer during the American Civil War. He was noted for his rapid rise in rank from a 1st Lieutenant at the start of the war up to a major general (two stars). His close association with General Ulysses S. Grant had him transferred from command of an infantry division in the western theater (Kentucky, Tennessee, Mississippi) to lead the Cavalry Corps of the Army of the Potomac in the east. In 1864, he defeated Confederate forces in the Shenandoah Valley in Virginia and his destruction of the economic infrastructure of the Valley, called “The Burning” by the residents, was one of the first uses of scorched earth tactics in the war. His cavalry units pursued Confederate General Robert E. Lee retreating forces and was instrumental in forcing Lee’s surrender at the Appomattox Courthouse in Virginia on 9 April 1865.
The first pilot model of the AR/AAV was delivered in June 1962. The aluminum hull vehicle had a conventional style driver’s hatch on the center line of the hull and it had water jet propulsion for amphibious operations. The large surfboard on the front hull was intended to prevent swamping while swimming in water.
This is the 12th XM551 pilot (and the last) delivered in February 1965. The front hull was redesigned where a rotating driver’s hatch replaced the earlier conventional hatch. This gave the driver excellent visibility without requiring him to lift his head above the plane of the hull. Note the new two piece folding surfboard and the folding flotation screens stowed along the top edges of the hull.
In order to kept the weight to a minimum and for the Sheridan to meet the amphibious and airborne requirements, the M551 hull was constructed of welded 7039 aluminum alloy armor plate, the same used on the M113 Armored Personnel Carrier. The turret, however, was made of steel armor. A layer of high density foam encased the basic hull which was an effort to improve flotation. Covering the foam was a thin aluminum skin on the exterior of the hull. The water jet propulsion was eliminated from the design and the tank was propelled in the water by it tracks.
XM551 Pilot #12 during amphibious operation testing at Fort Knox in Kentucky.
A Sikorsky CH-54B Tarhe heavy lift helicopter, more commonly known as the “Flying Crane”, carrying an M551 Sheridan at the Redstone Arsenal in Alabama.
The Cadillac Armored Reconnaissance/Airborne Assault Vehicle met the US Army requirements of being both amphibious and air dropable. Despite its long official nomenclature, to the average person and most in the military, it was a tank. The Allison Division of General Motors built 1596 M551s starting in 1966, with the last Sheridan rolling off the Cleveland assembly line in 1970.
The main armament of the M551 was an advanced 152mm gun/launcher designed to launch the Ford MGM-51 Shillelagh anti-tank guided missile or fire conventional ammunition. The missile carried a 15 pound (6.8 kg) shaped charge warhead which included 8 pounds (3.6 kg) of Octol explosives and had a maximum range of 2200 yards (2000 meters). Aiming the missile was simple where the gunner simply kept his gun sight on the target, while electronics in the sighting system tracked the missile optically and sent corrections through an IR link (similar to a TV remote control) to the missile in flight. The main problem with the system was the recoil from firing the main gun with conventional ammunition which threw off the missile optics.
This is the 24th production M551 at Aberdeen Proving Grounds shortly after it was delivered in 1966. It shows the infrared missile optics lenses on front of the box on top of the main gun.
XM551 Pilot #12 launches a Shillelagh anti-tank missile during testing in October 1967.
The 152mm gun/launcher was designed primarily as a missile launcher, with the gun aspect as secondary. With a large bore and no muzzle break on a short barrel, when firing conventional rounds the heavy recoil often caused the first one or two road wheels to lift off the ground. The conventional ammunition was not conventional at all. Instead of a metal cartridge shell case, the M551 used combustible cartridge cases. These cases had to be protected from moisture, even humidity, in order for them to stay together and completely burn. A removable bag system was developed where the loader stripped off the bag before the round was chambered. These relatively fragile rounds also posed a fire and explosion risk to the crew.
The XM551 pilots and the early production M551s main gun was designed with an Open Breech Scavenging System and bore evacuator. This system had the risk of blowing burning debris back into the vehicle and possibly igniting stowed rounds. This led to the redesigned Closed Breech Scavenging System (CBSS) that was factory installed beginning with production M551 number 700 and it was retrofitted to most of the earlier production M551s.
Basic Technical Data
|Crew||4 (Commander, Driver, Loader, Gunner)|
|Length||20 ft, 6 in (6.29 m)|
|Width||9 ft, 2 in (2.81 m)|
|Height||9 ft, 6 in (2.94 m), not including ACAV gun shield|
|25.4-31.7mm aluminum + ~20mm bolt-on steel front, 19-25.4mm aluminum sides, 12.7-19mm aluminum rear and roof|
|25.4-31.7mm steel front & mantlet, 25.4mm steel sides & rear, 19mm steel roof, ~20mm steel ACAV MG shield|
|Total Weight||15.2 tons (34000 lbs)|
|Propulsion||Detroit 6V53T 6 cylinder supercharged diesel 300 HP (220 kW)|
|Top speed||43 mph (76 km/h) road, 3.6 mph (5.79 km/h) in water|
|Range||348 miles (560 km)|
|152mm (5.98 in) M81 or M81E1 gun/launcher|
Normal load (20 rounds, 9 missiles), Vietnam load (>30 rounds of HEAT/Canister; no missiles)
|Secondary Armament||1x Cal.50 (12.7 mm) M2HB MG (AA mount; 1100 rounds), 1x Cal.30 (7.62 mm) M73 MG (coaxial mount; 3200 rounds)|
|Smoke||8x Smoke Grenade Launchers|
|Production||1662 (all combined)|
|XM551||Prototypes, 12 pilot models built|
|M551||Main Production Model|
|M551A1||Fitted with AN/VVG-1 laser range finder mounted in front of Commander’s cupola.|
|M551A1 (TTS)||(Tank Thermal Sight) – Fitted with AN/VSG-2B thermal sight unit.|
|M551 (NTC)||(National Training Center) – Modified mock-up enemy vehicles for training.|
Walk around: Prime Portal M551
Video: M551 Sheridan walk around
Since 1966, the US Army staff in Washington had been recommending to General Westmoreland (then commander of US forces in South Vietnam) that the M551 should be deployed to southeast Asia. Since the main gun ammunition was not available, he argued that it was simply a machine gun platform. By 1968, the new, or soon to be, US commander in South Vietnam, General Creighton Abrams, had been notified that the 152mm shells were finally available for the M551. However, as General Abrams began to make preparations for the re-equipping of US cavalry squadrons with the M551, the affected squadrons expressed their concerns that the new aluminum armored tank was not only highly vulnerable to land mines and rocket Propelled Grenades (RPG), that they would not be as effective at “jungle busting” compared to the heavier M48A3 Patton tanks. In late 1968, General Abrams met with Colonel George S. Patton IV (son of WWII General Patton), commander of the 11th Armored Cavalry Regiment (11 ACR). When Abrams mentioned the cavalry’s concerns over the new vehicle, Patton recommended that the M551s be combat tested by a divisional cavalry squadron as well as a squadron from his own regiment since the two squadrons had completely different missions.
Due to a lack of suitable targets, it was decided to remove the missile system from all the M551s which were being shipped to Vietnam and the expensive missiles were left behind. All but two of the guidance and fire control components of the missile system were removed. The power supply and rate sensor were retained because these were needed for stabilizing the turret. The resulting additional space was filled with two separate boxes, one for 7.62mm ammunition (coaxial machine gun), and one for 12.7mm (.50 MG) ammunition, and the missile stowage area was redesigned to accommodate conventional rounds.
The M81 152mm gun/launcher fired the following cartridges
M409 152mm HEAT-T-MP
M411 152mm TP-T (Training)
M596 152mm Dummy (Training)
M625 152mm Canister
M627 152mm HE-T
The M625 canister round was intended primarily for antipersonnel use at close range. The cartridge was loaded with 10000 13 grain steel flechettes and was very effective at cutting large swathes of jungle foliage. The official designation was the antipersonnel-tracer (APERS-T) round.
The first M551s began to arrive in South Vietnam in January 1969 and they were accompanied by their factory representatives, instructors and evaluators as the new vehicles were issued to the 3rd Squadron, 4th Cavalry Regiment, and the 1st Squadron, 11th ACR. By the end of 1970, there were more than 200 M551s employed in South Vietnam, and they stayed in the field until the last US armored cavalry unit, the 1st Squadron, 1st Cavalry Regiment redeploy back to the USA in April 1972. The M551s were found to be very effective in infantry support role, despite their slow reloading time. Their low ammunition load was sometimes compensated by accompanying M113 ACAVs which carried extra rounds on long patrols.
After being in country, the crews quickly modified their new mounts to increase their survivability in Vietnam. Gun shields used on the M113 Armored Cavalry Assault Vehicle (ACAV) were acquired and fitted to the tank commander’s .50 Cal machine gun and cupola. Many M551s mounted a AN/VSS-3 searchlight on the front of the turret to the left of the main gun. Since the M551 lacked internal space, many M551s had field fabricated extended bustle racks of various designs to hold extra ammo cans, rations and other equipment.
Often crewmen choose to ride on the outside of the M551 risking enemy fire to escape the heat and the threat of land mines. The driver was the unfortunate one who could not ride outside. To provide more protection from land mines, an Add-On Armor Kit was developed to add an extra layer of spaced steel armor bolted onto the bottom of the M551. It only covered the front half of the lower hull providing extra protection for the driver.
In January 1969, the US 25th Infantry division “Tropic Lightning” received thirty (30) M551 Sheridans. Twenty-seven (27) were assigned to the 3rd Squadron, 4th Cavalry Regiment “Mackenzie”s Raiders”, and three (3) were used as replacements. The 3/4 CAV had to trade their trustworthy combat proven heavy armored M48A3 Patton tanks for the new untested lighter armored M551 Sheridans. Training and transition to the M551 was completed in early February 1969.
The 3/4 CAV consisted of A, B and C Troops. D Troop was a air cavalry troop equipped with helicopters. The troop was denoted by a colored ring painted on the gun barrel, A Troop (Red), B Troop (White) and C Troop (Blue). The vehicles carried on the hull sides two large tactical numbers denoting the platoon number and the vehicle in the platoon number.
|A Troop (Red)|
1st, 2nd, 3rd Platoon
|B Troop (White)|
1st, 2nd, 3rd Platoon
|C Troop (Blue)|
1st, 2nd, 3rd Platoon
|A-10, A-20, A-30||B-10, B-20, B-30||C-10, C-20, C-30||Platoon Leader M113|
|A-11, A-21, A-31||B-11, B-21, B-31||C-11, C-21, C-31||Scout Section Leader M113|
|A-12, A-22, A-32||B-12, B-22, B-32||C-12, C-22, C-32||Scout Section M113|
|A-13, A-23, A-33||B-13, B-23, B-33||C-13, C-23, C-33||Scout Section Leader M113|
|A-14, A-24, A-34||B-14, B-24, B-34||C-14, C-24, C-34||Scout Section M113|
|A-15, A-25, A-35||B-15, B-25, B-35||C-15, C-25, C-35||Tank Section Leader M551|
|A-16, A-26, A-36||B-16, B-26, B-36||C-16, C-26, C-36||Tank Section M551|
|A-17, A-27, A-37||B-17, B-27, B-37||C-17, C-27, C-37||Tank Section M551|
|A-18, A-28, A-38||B-18, B-28, B-38||C-18, C-28, C-38||Infantry Section M113|
|A-19, A-29, A-39||B-19, B-29, B-39||C-19, C-29, C-39||Mortar Section |
M106 (107mm) or M125 (81mm)
Initially, the 4th CAV tank crews were not really pleased with the downgrade but the tankers opinion changed slightly after their first battle using the M551 Sheridan. On 10 March 1969, A Troop, 3rd Squadron, 4th Cavalry was bivouacked for the night at a road junction east of Tay Ninh City. A trooper manning a listening post suddenly heard movement in the darkness and quickly reported it to his superiors. Word was passed along the line to the tank crews in their M551 tanks. Using infrared night vision scopes, the tankers scanned the darkness for the enemy and spotted figures approaching their positions. The tank loaders chambered M625 “beehive” rounds and the gunners zeroed in their guns on enemy concentrations. The enemy continued to creep closer, unaware that they were targeted by tanks’ 152mm cannons. The cannon fire shattered the silence and the muzzle flashes lit up the night. Instantly thousands of sharp steel flechettes whizzed through the air, shredding jungle foliage and human flesh. Within minutes, the enemy attack came to a halt and wounded/surviving enemy faded back into the night. After daybreak, the US troopers swiped the battle area and found about 40 enemy bodies, including a battalion commander.
M551 A-15 has an unique elevated flat rack mounted on the rear hull carrying extra ammo cans.
This is another M551 A-15 with a different serial number which probably is a later replacement tank.
M551 A-16 also has an elevated flat rack mounted on the rear hull. A Jerry can is mounted on the end of the rack and another Jerry can is mounted on the rear hull.
This is another M551 A-16 which is probably a later replacement tank.
M551 A-17 has an additional .50 Cal machine gun mounted in front of the loader’s hatch.
M551 A-25 is parked in front of M113 ACAVs of the 2nd platoon. It was probably named after the 1968 Disney movie “The Love Bug” starring Dean Jones, Michele Lee and Buddy Hackett which is about an anthropomorphic racing Volkswagen Beetle named “Herbie”.
M551 A-36 sits in the mud at Landing Zone Hampton during a reconnaissance in force mission on 3 August 1969. Note the string of M18 smoke grenades hung on the side of the turret for quick use. The monsoon season in Vietnam generally began in mid-May and ends in late October/early November with the most rainfall in August and September. The lighter M551 was able to navigate through the mud better than the heavier M48A3 tank.
This is my close up of M551 A-36 showing the name “Sudden Death” on the gun barrel. A small framed section of fencing is mounted on top of the surfboard in front of the driver’s position with a couple spare track links next to it on the front hull. The tank commander is either studying a map or reading something.
M551 B-15 with Scout Section M113s B-11 and B-12 in the background.
M551 B-27 named “Hard Core 7” near Củ Chi (northwest of Saigon) on one of its first missions in February 1969. Some M551s of this unit had chained linked fencing mounted on the front of the tank intended as protection against RPGs. The fencing on the front hull would detonate the RPGs before hitting the tank’s armor but the driver probably would not survive the blast even with his hatch closed. The fencing is more likely intended to keep jungle foliage from cluttering the driver’s position.
M551 C-35 has a blue band (C Troop) on the gun barrel just behind the name “WOW”. Note the civilian cooler container sitting on the front hull.
The 11th Armored Cavalry Regiment (ACR), the “Blackhorse Regiment” consisted of three squadrons and was the only full armored cavalry regiment in Vietnam.
Structure of the 11th ACR in Vietnam
Headquarters and Headquarter Troop (HHT) 11th ACR (8 September 1966 to 5 March 1971)
1st Squadron (8 September 1966 to 5 March 1971)
- HHT, A Troop, B Troop, C Troop, D Troop, 1st Howitzer Battery
2nd Squadron (8 September 1966 to 6 April 1972)
- HHT, E Troop, F Troop, G Troop, H Troop, 2nd Howitzer Battery
3rd Squadron (12 August 1966 to 5 March 1971)
- HHT, I Troop, K Troop, L Troop, M Troop, 3rd Howitzer Battery
Note: The Howitzer Battery of each squadron was equipped with the M109 155mm SPH.
In January 1969, the 1st Squadron, 11th ACR began receiving the new M551 Sheridan. Up to that time, the ACAV troops were using the M113 ACAV and the M551 Sheridan was a definite improvement providing more firepower. One M551 replaced three M113 ACAVs in each platoon of the squadron.
In February 1969, the 1st Squadron, 11th ACR moved to Bien Hoa/Long Binh area to serve as a reaction force against an anticipated enemy attack. On February 23, the Viet Cong (VC) fired a heavy barrage of mortars and rockets against US positions. Perceiving this as preparation for a ground attack, Major William Privette, executive officer of the squadron, quickly assembled Troops A and B and a company of 1st Battalion, 2nd Infantry to make a sweep for the enemy. The task force immediately ran into a sizable superior enemy force. Privette formed both of his troops on a line and advanced. The front of the M551 tanks lifted about a foot and a half off the ground from the recoil of the 152mm gun. Overwhelmed by the massive firepower, the enemy attack broke and the enemy quickly retreated, leaving behind more than 80 bodies. This victory was only possible primarily because of the tank’s 152mm guns. A few months earlier with their M113 ACAVs, they would had engaged this superior enemy force with only their .50-caliber and 7.62mm machine guns. This was the first time the Blackhorse Regiment employed the M551 in combat and the tank crews were impressed.
After the enemy attack on Long Binh, troopers move pass a M551 Sheridan of the 1st Squadron, 11th ACR on 23 February 1969.
M551 A-37 of 11th ACR has a searchlight mounted. Note the field modified bustle rack on the rear of the turret. In front of the tank are canister rounds lying on the ground next to rows of MG ammo cans and other equipment waiting to be loaded.
M551 A-39 has mounted a gun shield for the commander’s .50 Cal MG which also has a flash suppressor. HEAT and canister rounds with combustible cartridge cases on the ground in front waiting to be loaded into the tank.
Photographed in February 1969, 11th ACR M551 named “The Devil Avenges” has an ACAV gun shield for the .50 Cal MG and a large field modified bustle rack on the rear of the turret filled with extra gear and supplies.
M551 of C Troop, 11 ACR near Loc Ninh (north of Long Binh) along the Cambodian border in 1969.
M551 named “Cloud Nine” of 3rd Squadron, 11th ACR in the rubber plantation area near Loc Ninh and Quan Loi on 17 October 1969.
A line of 11th ACR M551s halted on a road in the rubber plantation area on October 17. This photo probably taken from a helicopter flying overhead.
M551 named “Peace Pipe” has twin .50 Caliber MGs mounted with flash suppressors. The gun shield has “The Stalking Rhino” painted along the lower edge. On the front hull on both sides of the driver’s hatch are boxes of rations.
Although the M551 had some success, its greatest shortcoming was survivability. The aluminum alloy armor was not intended to repel anything heavier than a heavy machine gun round and it was highly vulnerable to the land mines and RPGs widely employed by enemy. The combustible cartridge cases of the 152mm shells was prone to detonating catastrophically when the vehicle was penetrated led to a low crew survival rate. Around one hundred M551s were lost in Vietnam, although some of these losses were due to breakdowns and overheating problems in the field.
Internal fire weakens the M551 aluminum hull and usually the heavy burnt steel turret would collapse.
This M551 damaged from an enemy land mine is missing a couple of road wheels.
The side of this M551 was damaged from enemy RPG fire.
A M578 Light Recovery Vehicle provides support to a broke down M551 Sheridan in the field.
The A-frame boom of a M88 Armored Recovery Vehicle (ARV) can lift the M551 completely off the ground. The M551 is probably from the 3/4 CAV indicated by the number on the side hull.
On 1 December 1969, the 1st Squadron, 1st Cavalry Regiment received the M551 Sheridan replacing their trustworthy M48A3 Patton tanks. The 1st Cavalry was attached to the US 23rd Infantry (Americal) Division with the 196th Infantry Brigade and operated around the Chu Lai area roughly 56 miles (90 km) southeast of Da Nang.
On 4 January 1970, Americal troops of B Company, 4th Battalion, 3rd infantry repelled an enemy mortar and sapper attack against their night defensive positions (NDP). After withstanding an intense mortar barrage and ground attack, the troopers killed 29 of the enemy. A Troop, 1st Squadron, 1st Cavalry combined with the 15th Regular Force Group (South Vietnamese) defeated about two companies VC. A Troop, while fighting in the area 3 miles (4.8 km) of Tam Ky (southeast of Da Nang) killed 43 of the enemy during the engagement.
On January 13 and 14, heavy fighting was reported in the 196th area of operations. A task force consisting of 1st Squadron, 1st Cavalry; 46th Infantry and 2nd Battalion, 1st Infantry, overran enemy positions killing 40 of the enemy and capturing a large ammunition cache. The 196th Brigade killed 662 NVA in action in the “Pineapple Forest” area near Tam Ky.
The squadron, terminated operations in the Quang Tin Province on 3 March 1970, known to the 196th Brigade as Operation Frederick Hill. The next two weeks, the squadron was in Chu Lai and on March 17 the squadron went on operational control to the 196th Brigade for an operation near LZ Ross.
M551 A-28 named “Diane” (on front of the missile tracking system box over the main gun) moves out while on an operation north of Tam Ky, 18 March 1970. “AMCAL” stands for the Americal Division.
The Cambodian campaign, also known as the Cambodian incursion and the Cambodian invasion, was a series of operations conducted in eastern Cambodia by South Vietnam and the US as an extension of the Vietnam and the Cambodian Civil Wars. Thirteen major operations were executed by the Army of the Republic of Vietnam (ARVN) between 29 April and 22 July and by US forces between 1 May and 30 June 1970.
The objective of the campaign was to eliminate supplies and troops of the People’s Army of Vietnam (PAVN) and the VC in the eastern border regions of Cambodia. Cambodian neutrality and military weakness made this country a sanctuary for the PAVN/VC forces allowing them to establish bases to support their operations in South Vietnam. At that time, the US was shifting toward a policy of Vietnamization (transferring the responsibility and the war effort to South Vietnam) and sought to strengthen South Vietnam by eliminating this border threat.
On 3 May 1970, a 11th ACR M551 along the Vietnam-Cambodian border near Prasaut, Cambodia. An officer standing in front is using binoculars to search for enemy forces. On the hull side is the US Cavalry crossed sabres emblem. Above the sabres is a number 11 and below the sabres is a number 2 for the 2nd Squadron.
Photo: Bettmann/Getty Images
On 18 May 1970, this M551 of A Troop (read band on gun barrel), 3rd Squadron, 4th Cavalry, 25th Infantry Division is on a search and destroy mission somewhere in Cambodia.
This is a Black/White photo of the same M551 above. Note that the red band on the gun barrel cannot be seen. On the hull side, the platoon number 3 can be seen.
This is M551 number 35 probably also of A Troop, 3/4 CAV in Cambodia.
A 11th ACR M551 with twin .50 Caliber MGs moving along a jungle trail in Cambodia, June 1970.
M551 A-29 named “ARIZONA” of 2nd Platoon, A Troop, 1st Squadron, 11th ACR after the Cambodian incursion in September 1970.
A M551 of the 11th ACR prepares to move from its blockade position on 23 January 1971. To the right of the registration number 12F37369 in the center of the hull is the name “Blessed One”. The loader has a field installed M60 MG with a gun shield taken from the M113 ACAV kit.
Dewey Canyon II
DEWEY CANYON II was the first phase of LAM SON 719 (8 February – 25 March 1971), a large offensive operation against NVA communications lines in Laos. LAM SON was the birthplace of a famous Vietnamese patriot who defeated an invading Chinese army in 1427. The numerical designation of 719 came by combining the year (1971) and the main highway to be used, Route 9. Because of the Cooper-Church Amendment passed by Congress in late 1970, US ground troops and advisers were prohibited from entering Laos. The ARVN would provide and command the ground forces that would enter Laos, while US Army and Air Force units provided aviation airlift and supporting firepower. The operation called for ARVN troops to drive west from Khe Sanh, cut the Ho Chi Minh Trail, seize Tchepone in Laos and, after destroying NVA forces and supplies, return to Vietnam. The first part of the operation (Phase 1), which began at 0400 hours on 29 January 1971, was conducted by US ground forces, in large part made up of the 1st Brigade, 5th Mechanized Division. Its mission was to open Route 9 to the Laotian border.
The vanguard of the 5th Infantry Division, an armored cavalry/engineer task force, cleared the road from Vandegrift Combat Base (southwest of Cam Lo in the region south of the DMZ) along highway Route 9 toward Khe Sanh. The area was cleared so that 20000 ARVN troops could reoccupy 1000 square miles of territory in northwest South Vietnam and mass at the Laotian border in preparation for the invasion of Laos.
US forces earmarked for this operation included: four battalions of the 108th Artillery Group; two battalions of the 45th Engineer Group; the 101st Airborne Division; six battalions of the 101st Aviation Group; the 1st Brigade of the 5th Infantry Division (reinforced by two mechanized, one cavalry, one tank, and one airmobile infantry battalions; and two battalions of the 11th Infantry Brigade, 23rd Infantry (Americal) Division.
On 3 February 1971, a M551 of 1st Squadron, 1st Cavalry near the Laotian border at the former Lang Vei Special Forces camp providing cover to elements of the Americal Division. The trooper standing on top of the turret is flashing a v-sign. Note this M551 is missing a road wheel.
On 7 February 1971, a M551 Sheridan tank is perched on a hill near Khe Sanh. US troopers are standing next to the tank around a burnt out camp fire.
This is my close up of the M551 above. Two tank crewmen have the M551 engine grills open and probably pouring water from Jerry cans into the tank’s radiator. On the rear hull side, the yellow triangle is the tactical marking of A Troop, 3rd Squadron, 5th Cavalry. Two red numbers on the triangle indicate the platoon and vehicle number which in this photo is obscured by the dried mud.
US troopers rest beside M551 named “WAR DADDY” of the 3/5 CAV in 1971. Underneath the missile tracker/system box, barely visible in small text is “THE END OF THE LINE”. The white solid circle on the rear of the hull would indicate the M551 belonged to C Troop.
A M551 Sheridan helps tow trucks of a supply column along Route 9. Behind the M551 is a M62 or M543 5-ton, 6×6, wrecker which is towing a damaged M54 cargo truck carrying artillery shells.
US M113s and a Sheridan is covering ARVN units moving to the Laotian border along Route 9. In the foreground on the right is an ARVN M41 tank. The M551 is facing Route 9 with its turret pointing to its rear. A canvas cover is erected beside the M551 as cover for the crew.
11th ACR 1972
During the withdrawal of US forces from Vietnam, the 11th ACR was inactivated in stages. The 1st and 3rd Squadrons were inactivated and left Vietnam in 1971 while the 2nd Squadron soldiered on in Vietnam into early 1972.
M551 G37 of 3rd Platoon, 2nd Squadron, 11th ACR about to leave an interior fuel and supply point somewhere in the Tan Uyen District in February 1972. This M551 is interesting because the flotation screen compartment along the edges of left side of the hull has been completely removed.
Photo: Doug Kibbey
M551 of G Troop, 2/11th ACR refueling at an night defensive perimeter. Note the M60 MG at mounted at the loader’s hatch. An artillery ordnance container is used to extend exhaust stack directing the exhaust flumes above the crew and gear. An early “self-service” aerial-delivered fuel blivet with a hand pump for diesel fuel is being used.
Photo: Doug Kibbey
This is the rear of M551 G39 showing its field fabricated bustle rack and rear hull covered with extra gear which the crew had accumulated. On the rear hull is a roll of chain linked fencing which would be erected around the tank at night to protect it from RPGs. G39 was later knocked out by a line mine and was towed back to base.
Photo: Doug Kibbey
Since the prototypes, the gun sighting system used on the M551 had always gave the gunner constant problems. In 1971, Hughes Aircraft was contracted to develop the AN/VVG1 Laser range finder for use on the Sheridan. Vehicles that had it installed were re-designated as the M551A1. They are visually distinguished from the earlier models by the laser mounted beneath the tank commander’s machine gun mount.
In 1977, a Product Improvement Program (PIP) was launched to update the Sheridan and address certain problems found in combat. The original tow lugs, made of aluminum and welded to the hull, were prone to be torn off in combat. They were replaced with steel tow lugs which penetrated the hull and were bolted to steel back plates. Also, a more robust drive sprocket was installed and the slave starting receptacle was relocated from inside the vehicle to a position on the outside of the front hull. The old aluminum block 6V53T Detroit diesel engines were replaced with newer visions with cast iron blocks, improved turbo superchargers, and an improved throttle control. This unfortunately increased the weight, but it gained improved reliability, increased performance, and less noticeable exhaust flumes. Later, newer style cluster smoke grenade launchers replaced the original individual ones on the turret and the M240 7.62mm coaxial machine gun replaced the earlier M73/M219 coaxial machine guns.
The 3rd Battalion, 73rd Armor Regiment (Airborne) was equipped with M551 Sheridans and LAV-25 8-wheeled armored reconnaissance vehicles which provided the US 82nd Airborne Division with light armor support. Although the US Army was phasing the M551 Sheridan out of regular armored units, the 82nd Airborne had kept it in service because there was no other vehicle available which could replace it.
A C-130 drops a M551 tank using the Low Altitude Parachute Extraction System (LAPES).
In 1979, the US Army opened the National Training Center (NTC) at Fort Irwin, around 100 miles (160.9 km) northeast of Los Angeles, California. The desert environment provided troops the space to use tanks, howitzers and other heavy weapons in large, conventional training exercises. To make these exercises more realistic, a number of captured Soviet vehicles were obtained, including at least one tracked MT-LB armored personnel carrier and a BTR-60 wheeled troop carrier. But there were not enough of these real examples to form large fictitious enemy units. So the US Army introduced its “visually modified” tanks and armored vehicles which were commonly referred to as VISMODs.
The first VISMODs were based on the M551A1 which gave the Sheridan a new purpose. With the help of numerous cosmetic add-ons made of sheet metal, plywood and fiberglass components, the Sheridans were made up to play the role of Soviet T-72 tanks, BMP-1 armored personnel carriers, self-propelled howitzers, and ZSU-23-4 mobile anti-aircraft guns. Each vehicle was equipped with sensors indicating its “guns” firing and to pick up signals if the vehicle had been hit by a simulated round. A light mounted on the vehicle would light up indicating it was knocked out.
On the NTC battlefield, the Opposing Force (OPFOR) was portrayed by the fictitious, Guards 60th Motorized Rifle Division, which was based on Soviet Army structure and doctrine. All members of the OPFOR units wore Soviet uniforms and were equipped with Soviet weapons. Visiting armored units who “fought” against the NTC OPFOR units found them to be a formidable force.
A M551A1 VISMOD T-72 tank at the National Training Center in 1984.
The M551A1 VISMOD BMP-1 had the 152mm gun barrel removed. A dummy 73mm gun and a launcher rail with a Sagger anti-tank guided missile (ATGM) was added.
A M551A1 VISMOD ZSU-23-4 at the National Training Center.
A M551A1 VISMOD Soviet 122mm self-propelled howitzer.
A M551A1 VISMOD Soviet T-80 tank during the early 1990s.
The Sheridan VISMODs were also prone to break downs at the NTC. A M88A1 Armored Recovery Vehicle tows two M551 VISMOD BMP-1s back for repairs.
The M551A1 Sheridan VISMODs were retired from the National Training Center in 2003.
The US invasion of Panama, code named Operation Just Cause, lasted over a month from mid-December 1989 to late January 1990. The primary purpose of the invasion was to overthrow the Panamanian dictator, Manuel Antonio Noriega Moreno on charges of racketeering, drug smuggling, and money laundering. Noriega’s rule in Panama was marked by repression of the media, an expansion of the military, and the persecution of his political opponents, and effectively controlling the outcomes of all elections. He relied upon his military to maintain his power, and did not follow any specific social or economic ideology. Noriega was known for his complicated relationship with the US, being described as being its ally and nemesis simultaneously.
The Panamanian Defense Forces (PDF) consisted of only two infantry battalions and ten independent infantry companies. Armor support was 38 US built Cadillac Gage armored cars. The first of these vehicles arrived in Panama from the USA in 1973, consisting of 12 of the V-150 APC variant, and four V-150(90)s with 20mm gun turrets. In 1983, another delivery arrived consisting of three V-300 Mk.2 IFV variants, and nine V-300 APCs, including a Command Post vehicle and an ARV vehicle. The three V-300 Mk.2 IFVs were fitted with the Cockerill CM-90 turret and a 90mm gun imported from Belgium. The PDF had a genuine anti-tank threat which had to be contended with.
In April 1989, US President George H. W. Bush launched Operation Nimrod Dancer which deployed additional US forces to Panama to protect US citizens/possessions and to present a show of force in Panama.
US units deployed to Panama during Operation Nimrod Dancer were:
- Brigade Headquarters
- a Light Infantry Battalion from US 7th Infantry Division
- a Mechanized Infantry Battalion from US 5th Mechanized Infantry Division equipped with M113 APCs.
- a Marine light armored company equipped with LAV-25 Light Armored Vehicles
On November 15 while the diplomatic effort was failing, a group of M551A1 Sheridans from C Company, 3-73 Armor, US 82nd Airborne Division was loaded onto a C-5A Galaxy transport aircraft for deployment to Panama. This contingent was made up of 4 tanks and a command and control unit. These tanks arrived on the 16th at Howard Air Force Base and were kept in a hanger to conceal their presence from any prying eyes. The 82nd Airborne markings were removed from the tanks. Tank support for the upcoming invasion was recognized as vital, as PDF had a small armored force which could interfere with the invasion. The plan for the use of these four tanks was to work with a platoon of USMC LAV-25s to conduct reconnaissance operations under the unsubtle name “Team Armor”.
Beside the four tanks in situ in Panama, an “armor ready company” size element of 10 Sheridans was prepared at Fort Bragg, North Carolina to accompany and support the deployment of the 504th Parachute Infantry Regiment. As such, four of these Sheridans were fitted for low-velocity air delivery (LVAD) via a C-141, while the other six tanks were prepared for air delivery to be rolled out of the aircraft that had landed. This would be the first time the Sheridan was ever air dropped in combat and probably the only combat air drop of tanks in history.
For the Sheridans used in the invasion required the fitting of .50 Caliber heavy machine guns onto the mounts on the turrets and the loading of Shillelagh missiles. It is noteworthy that rules of engagement given to crews of the Sheridans were that approval for firing the main gun had to be sought from, and given by, the task force commander due to the high risk of hitting friendly troops, civilians or causing collateral damage.
On 15 December 1989, Noriega declared that a state of war existed with the USA in retaliation for the banning of Panamanian ships from US harbors. The next day, the PDF shot to death an unarmed US serviceman, wounded another, seized and beaten another serviceman, and sexually threatened his wife. Under these circumstances, President Bush decided that he must act to prevent further violence.
On 20 December 1989, the US 82nd Airborne Division conducted their last combat jump at Torrijos International Airport, Panama. The 82nd Airborne Division’s previous combat jump was 45 years earlier during Operation Market Garden in September 1944.
Shortly after the Airport was captured, low-flying C-130 transports made the airdrop of the heavy equipment consisting of M551 Sheridans and M998 HMMWVs These vehicles were dropped away from the troops for fear of the obvious consequences of dropping both in the same place. This led to a delay in recovery of the vehicles, which was not finished until 0900 hours, with some of them found outside the airport in the tall grass.
This 82nd Airborne M551A1 was destroyed after its parachute(s) failed to deploy. The impact did major damage to the Sheridan’s suspension and lower hull. Luckily, the tank crew was riding not inside in the drop. Another Sheridan was also damaged in the drop but was repairable.
Task Force Bayonet consisted of the 193rd Infantry Brigade (command of the TF), elements of the 4th Battalion, 6th Infantry Regiment, 5th Mechanized Division, the four M551A1 Sheridan (secretly brought in country), and various military police units. The task force’s objectives was the Headquarters of the PDF (La Comandancia) followed by securing the Fort Amador and seizing the Balboa DENI Station (Police HQ) and then to secure the US Embassy.
One of the Sheridans in an armor column of Task Force Bayonet advancing towards La Comandancia. Following behind the Sheridan is a LAV-25. Note the bumper code of the M113 in the foreground, 5-4-6 (5th Div – 4th Bat – 6th Inf Reg).
This is my close up of the Sheridan above. The loader appears to be holding a WWII era M3 .45 Caliber submachine gun commonly referred to as the “Grease Gun”.
As US forces closed in on La Comandancia, resistance became more fierce and a column of three M113s moving up to the outside wall in order to plant charges to force an entry was repeatedly hit by around 20 rounds of what was believed to be enemy fire. The lead M113 suffered such damage that it was disabled and the second one was knocked out and set on fire. The infantry platoons of three M113s had to pile into a single vehicle with several men wounded in order to evacuate from the area. Later it was discovered that the column was hit by 40mm fire from a USAF AC-130H Spectre gunship, which had mistaken the M113s as enemy armored vehicles. This was compounded by smoke from fires from the compound and, rather than risk further friendly fire incidents, fire support was received from Quarry Heights around 450 meters (492 yards) away. This fire support came from USMC LAVs firing 25mm cannons, and 152mm gun fire from two M551A1s positioned on Ancon Hill. The M551A1s fired only 13 rounds. Just like with the AC-130H, the smoke obscured the target to such an extent that even they were ordered to cease fire for risk of collateral damage or civilian deaths.
Stop the music
Huge efforts had been made to cover all possible routes which Noriega could escape from the country, however on December 20th the US had no idea where he was. They had missed the chance to capture him when the car he was riding in went past a US roadblock. Noriega’s non-capture would been a serious embarrassment to the whole operation. Fearing Noriega may take refuge in the embassy of an unfriendly nation, like Nicaragua, Cuba, or Libya, where US forces could not touch him, those areas were tightly sealed off by US forces. While the massive manhunt was underway, diplomatic envoy (Papal Nuncio) of Pope John Paul II acting for the Vatican City, Monsignor Laboa, gave Noriega asylum in their embassy on Christmas Day 1989.
As soon as the US commanders had learn of where Noriega was located, they only had one option and sealed off the Vatican Embassy so that no one could go in or out and then tried to solve the situation diplomatically. With civilians chanting against Noriega outside the Vatican Embassy, it was decided to force him out with Rock and Roll. Very loud rock and roll music was blasted through large speakers courtesy of broadcasting US Military Radio for Central America (Southern Command Network), with the song selections came from many of the US personnel in the area. The music selected was lyrical compositions of Guns ‘n’ Roses, Jethro Tull, The Clash, Alice Cooper, Black Sabbath, Bon Jovi, The Doors, and AC/DC. No one inside would been able to think, talk or sleep with this appalling racket blasting outside around the clock. After days of this, the situation was handed off to the 4th Psychological Operations Group but shortly afterwards, the music stopped. Noriega had nowhere to go and the Vatican wanted the situation quickly resolved. On 3 January 1990, Noriega walked out of the embassy gate accompanied by three priests and surrendered to US forces.
Crewmen of this Sheridan are using binoculars to scan the buildings surrounding the Vatican embassy along Balboa Avenue in Panama City on 28 December 1989.
Photo: BOB PEARSON/AFP via Getty Images
A US soldier searches the pack of a Papal courier outside the Vatican embassy on December 28. The M551 Sheridan in the background is manning a roadblock.
Photo: BOB PEARSON/AFP via Getty Images
This M551 at a roadblock in Panama City is an early production vehicle with the Open Breech Scavenging System gun tube and bore evacuator.
A M551 at a roadblock in Panama City on 1 January 1990. This is probably the same M551 in the above photo.
In the early morning hours of 2 August 1990, Iraqi dictator Saddam Hussein launched an overwhelming invasion of Kuwait. For the US government and President George Bush, the first priority quickly became the defense of Saudi Arabia. Disruption of Kuwaiti oil supplies was damaging enough to the global economy and disruption of Saudi oil supplies could be disastrous.
On 8 August 1990, the first units of the US XVIII Airborne Corps began deploying to Saudi Arabia. The US 82nd Airborne Division ready brigade’s rapid deployment clearly signaled a US national commitment to counter any further Iraqi aggression. The brigade brought its light anti-tank weapons and M551 Sheridans of the 3rd Battalion, 73rd Airborne Armor Regiment which provided some anti-armor capability with its 152mm gun and Shillelagh antitank missiles. The paratroopers would been at considerable risk if Saddam Hussein decided to invade Saudi Arabia before the US completed its force buildup.
The first M551A1s to arrive in Saudi Arabia were flown in from their European bases on C-5 Galaxies still painted in their NATO green camouflage. Due the 120 degree heat in Saudi Arabia, all soldiers had to keep hydrated by consuming large quantities of water throughout the day.
During desert training in Saudi Arabia, many of the M551 Sheridans were hastily smeared with wet sand to blend them into the desert background.
The 56 M551A1 Sheridans used by the 3-73 Armor in Desert Storm were specially modified with the installation of the Tank Thermal Sight (TTS) from the M60A3 tank at the Anniston Army Tank Depot, which concurrently overhauled and repainted the vehicles. The modified vehicles replaced the M551s that were already in Saudi Arabia during November and December 1990.
After the Desert Storm air war began on 17 January 1991, the modified M551A1s were re-positioned in theater by C-130H transports, where one is being loaded here.
For the Desert Storm Operation, US 82nd Airborne Division was positioned in the area southeast of the Rafha Airport located along the northwest border of Saudi Arabia. On 24 February 1991, the 82nd Airborne supported by the Sheridans of the 3-73 Armor crossed the border into Iraq and made a dash towards the As Salman Airbase located in Southern Iraq approximately 294 km (183 miles) south of Baghdad.
This 3-73 Armor M551 Sheridan is driving along a desert road during the advance. On the hull side is the Coalition invasion marking (^). Note that this M551A1 is missing a road wheel.
Crews of M551 Sheridans taking a rest break during the invasion.
The Sheridan fired the Shillelagh missile in combat only in Desert Storm, and fewer than a half dozen were fired compared to the thousands of conventional rounds fired in Vietnam, Panama and Desert Storm total. It is believed that an Iraqi anti-tank gun position was destroyed with a single Shillelagh missile during Desert Storm which would been the only combat victory for the Ford built anti-tank missile. Some sources state that a Sheridan did destroyed a single Iraqi tank but there is no confirmation of this.
A M551A1 Sheridan of 2nd Platoon, B Troop, 3-73rd Armor carrying 82nd paratroopers passes a burnt out Iraqi tank. The Iraqi tank is a Type-59-B or Type 69 identified by the skirts, light guard, and rear hull.
M551A1 Sheridan of A Troop, 3-73rd Armor guarding the main gate of Tallil Air Base in southern Iraq on 3 March 1991 the day after the cease fire.
M551 Bridge Layer?
During the development of the XM551 Sheridan, a proposal for a bridge layer vehicle based on the M551 chassis was conceived and submitted. The M551 bridge layer vehicle never went into production. Instead in 1966, the US Military Assistance Command, Vietnam (MACV) made a request for a lighter more mobile vehicle-launched bridge. This resulted in 20 M113 Marginal Terrain Assault Bridge Launchers (MTAB-L) being built and deployed to Vietnam in mid-1968.
On 19 May 1995, the movie “Die Hard with a Vengeance” starring Bruce Willis, Jeremy Irons and Samuel L. Jackson was released in the US. This is the third film in the Die Hard film series.
A M551 Bridge Layer is in the scene where the villain “Simon” (Jeremy Irons) and his cohorts masquerading as construction workers excavate Wall Street in New York city to break into the basement vaults of the Federal Reserve Bank of New York Building which hold $140 billion of gold bullion. The bridge section was placed in the dug trench and used as a ramp for a tunneling machine to drive down into the sewer seen in the next scene.
There is no information where the M551 Bridge Layer came from or if it is an authentic vehicle. It could be a one of a kind fabricated engineer vehicle from a US Army or National Guard unit, or maybe its just a mock up vehicle made for the movie.
Movie Clip: Die Hard With A Vengeance: Bank Invasion
During the late 1990s as the US Army was disposing its excess inventory, many of the M551 Sheridans were scrapped but a number of them were donated to the Artificial Reef Program. The program used the obsolete US Army armored vehicles as materials to build artificial reefs off the US eastern coast.
Armored vehicles from Forts Stewart and Benning in Georgia and from Anniston Army Depot in Alabama including M60 tanks, M113 APCs and M551 Sheridans were stripped for spare parts, drained of their polluting fluids, and steamed cleaned at Fort Dix, New Jersey. Then they were transported to barges at the Earle Naval Weapons Station on the New Jersey shore before being dumped into 50 feet (15.24 meters) of ocean off the New York, New Jersey, Delaware, Maryland and Virginia coasts.
The tanks and APCs would form patch reefs where the water is green and rich in algae and plankton but where natural reefs did not exist. Fish would start to colonize, and hide from predators, within days after the tanks hit bottom. Triggerfish, baitfish, and round herring would school up over the high structures of the armor vehicles. It takes four or five years for a reef to develop the thick layer of vegetation and the small sea animals to feed a lot of fish.
A barge carrying M551 Sheridans on their last voyage.
On Sunday 18 August 1996, the M551 Sheridans were pushed off the barge plunging into the sea sinking to their final resting place off the coast of Virginia.
Video: M551 Sheridan in Motion!!
MODEL KITS AND DECALS
Tamiya 36213 U.S. Airborne Tank M551 Sheridan Display Model – 2019
Echelon Fine Details Decals:
D166264 M551s in Vietnam (Part 1)
D166266 M551s in Vietnam (Part 2)
Tamiya 35365 M551 Sheridan Vietnam War – 2019
Academy 13011 US Airborne Tank M551 SHERIDAN – 2005
Academy 13208 M551 Sheridan Gulf War – 2007
FC Model Trend 35501 11th ACR M551 Sheridan twin MG mounts – 2018
FC Model Trend 35543 M551 Sheridan Vietnam rear turret basket – 2019
Echelon Fine Details Decals:
D356262 4/12 CAV M551s & M113s in Vietnam
D356263 3/5 CAV M551s & M113s in Vietnam
D356264 11 ACR M551s & M113s in Vietnam (Part 1)
D356265 11 ACR M551s & M113s in Vietnam (Part 2)
D356266 3/4 CAV M551s & M113s in Vietnam (Part 1)
D356267 3/4 CAV M551s & M113s in Vietnam (Part 2)
D356268 1/1 CAV M551s & M113s in Vietnam (Part 2)
D356269 11 ACR M551s & M113s in Vietnam (Part 3)
FOX MODELS D035026 M551 Sheridan Decal Set (1) Vietnam War – 2019
Mec Models DE-SH01 M551 Decals – 2010
S-Model (China) PS720027 M551 Sheridan (Early Version) – 2013