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M551 Sheridan
A Troop Reflections on the Sheridan

Write-up on the Sheridan from J.T. Tillman

In late 1952 the Army decided to begin development on a new vehicle to fill the requirement for an air transportable/ deployable light tank. Two vehicle prototypes, the T71 and T92, were considered but they both mounted the 76 mm main gun, and this was considered inadequate for the current Soviet armor. A new vehicle was needed that would have to be light enough to be air dropped with an armament system capable of handling potential opponents. In the Spring of 1960 General Motors was selected for development of the new Armored Reconnaissance/Airborne Assault Vehicle (ARAAV), designated the XM551. Production of the vehicle, now called the M551 General Sheridan, began in 1965. M551

This vehicle weighed in at 17 tons, combat loaded. Power for the vehicle was provided by a 300 horsepower V6 water-cooled, turbo-charged diesel engine that was coupled to a six speed transmission (four forward and two reverse gears) giving the vehicle a top speed of 43 miles per hour. The 160-gallon fuel tank gave the M551 a range of 373 miles. There was a fixed fire extinguisher system for the engine compartment that could be activated by the driver or from an outside pull handle on the left side of the vehicle above the first two road wheels.Data Sheet for the M551

photo right: Shows the rear of the turret of a Sheridan, with duster cans, mermite cans, 5 gallon water cans, and other assorted items strapped to the turret. It sure beat walking to work with a light infantry unit where the troopers had to carry everything on their backs, but there was precious little room for luxury items and some of the extra things which we would have liked to take with us. Good

Photo below: The Armored Reconaissance Airborne Assault Vehicle, M-551, or "Sheridan Tank." As can be seen in this picture, the vehicle was relatively small, and the maintenance tasks were not as demanding as on the larger, heavier M-48 tanks.Good

The suspension system consisted of five sets of road wheels on each side mounted on a torsion bar suspension with a rear drive sprocket and front idler wheel. There were no track return rollers, and the first and last sets of road wheels were fitted with hydraulic shock absorbers.Line drawings 

Armament consisted of a 152mm (6-inch) main gun that could fire both combustible case conventional ammunition and high explosive Shillelagh missiles. However, the missile system was not put in the M551's that were sent to Vietnam. The conventional ammunition fired from the vehicle consisted of High Explosive (HE), High Explosive Anti-Tank (HEAT), (diagram of HE and HEAT rounds) White Phosphorus (WP) and Cannister (affectionately referred to as "can rounds" by the Sheridan crewmembers). It's interesting to note that the Vietnam War brought about the invention of the Cannister round making necessity the mother of invention. (diagram of cannister round). The tank commander had an M2, Heavy Barrel (HB), .50 caliber machine gun to fire, and there was an M73, 7.62mm machine gun mounted coaxially inside the turret for the gunner to fire. Smoke grenade launchers that were used for cover were fitted on the underside of the forward position of the turret, but these were never used in the Vietnam War. Internal workings

Sheridans were sent to Vietnam in January 1969 for a field test. They were assigned to the 3rd Squadron, 4th Cavalry of the 25th Infantry Division and the 1st Squadron, 11th Armored Cavalry Regiment. This test ran for three months with several problems noted. The two biggest problems were the vehicles being severely damaged after running over mines and the conventional ammunition inside the turret rupturing and detonating after the vehicles were hit by RPGs. A partial solution for the mines was the installation of "belly armor" - titanium armor panels placed under the bow of the hull. However, there was no real solution to the RPG problem other than for the crewmen, except the driver, to ride on top of the vehicle's turret for added safety. Specifications

Water Crossing photos contributed by Super Sport:
Preparing Sheridan for Crossing Water
Sheridan crossing water

Even with these problems M551 Sheridans were sent to all of the divisional cavalry squadrons and the rest of the 11th Armored Cavalry Regiment in Vietnam. The Sheridans saw quite a bit of action and were instrumental in racking up some high body counts. They were some of the last armored vehicles to be withdrawn from Vietnam in the early 1970's. Their last major action was during early 1971 when Sheridans from A Troop, 4/12th Cav and from the 3/5th Cav supported ARVN forces engaged in Operation LAM SON 719.

It's interesting to note that Electro-Optical Systems (a Xerox company), the company that manufactured the telescopes and night vision devices for the Sheridan, nicknamed the vehicle the Stalking Rhino. Crewmen were given Stalking Rhino patches that were sewn on the upper left pockets of their jungle fatigue shirts.

Being the innovative, scrounging, resourceful, fire power hungry Cav troopers that they were, Sheridan tankers in Vietnam managed to come up with some serious additions of armament for their vehicles. It wasn't uncommon to see an M551 with dual .50 caliber machine guns mounted in front of the tank commander's position, an M60 machine gun with butterfly grips or another .50 caliber machine gun mounted in front of the loader's hatch or even a 40mm Hughes grenade launcher mounted somewhere on top of the turret. But hey, they were the Cav!!!

Photo above right: A frontal view of a Sheridan, showing how the external spaces on the turret were used to carry extra ammunition, food, and other essentials for extended stays in the field.Good

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This site is in no way connected to, or sanctioned by, any official Army or Government entity. This is, and will be a work in progress; we apologize now for any errors and/or mistakes. Information for this site has been and will continue to be gathered from many different sources. It is intended as a place for fellow troopers, family and friends of A Troop 4th Squadron 12th Cavalry (Vietnam Era) to visit, seek contact with, gather information or some insight into the history, language and jargon of the people who were part of A Troop, then and now. A Troop 4/12 Cav (Vietnam Era) invites and encourages trooper's family members to participate in the troop's reunions, memorial services, remembrances of our fellow troopers who have passed on to Fiddler's Green, and to continue the camaraderie of the BROTHERHOOD....Long Live the Cav and its BROTHERHOOD!!