The Ford Shillelagh
8 x MGM-51 Shillelagh ready-to-fire missiles would have been standard but their cost and lack of targets in Vietnam meant that they weren't even shipped to the theater. The Shillelagh was development of Ford and proved expensive and somewhat of a disappointment in the end. Despite it being made available by the time of the Vietnam War, the missile was not even used in anger until the Gulf War in 1990, to which the missile was unleashed successfully on Iraqi fortified bunkers (on at least two reported occasions). Despite the anti-tank prowess of the missile's design, the Sheridan was still a "light" tank and no match for squaring off head-to-head against modern Soviet T-72s in the conflict. As such, their role still remained that of reconnaissance. Though some 88,000 Shillelagh missiles were produced, barely a fraction of these were ever fired. The BGM-71 TOW's arrival made sure that the Shillelagh was all but extinct.
Additionally, crew protection was served through 1 x 12.7mm M2HB heavy commander's heavy machine gun and a 1 x 7.62mm co-axial machine gun (early models were fitted with the M73/M219 co-axial system whilst later ones had the M240C system in its place). The 12.7mm machine gun was affixed to the commander's cupola while the 7.62mm armament was fitted as a co-axial unit alongside the main gun and operated by the gunner. While early Sheridans sported protection-less machine gun cupolas, many Sheridans in Vietnam added M113 APC-type ACAV machine gun "shields" to their .50 caliber stations. Others also made use of an additional external M60 7.62mm machine gun for the loader (some complete with applicable ACAV shielding), an additional M2HB .50 caliber heavy machine gun as well as searchlights later added. 8 x smoke grenade dischargers were set to the front sides of the turret, four in a row to a turret side.
Sheridans in Vietnam
As early as 1966 there was talk of sending these new tanks to the combat warzones of Vietnam, Army personnel eager to see how the new system would fare. However, delays were almost inevitable with the type's specialized ammunition and armament. Additionally, while the Germans in World War 2 and the Soviets/North Koreans in the Cold War maintained a substantial collection of armored vehicles for which the high-priced Shillelagh missile was designed to defeat, it was a different matter in the jungles of Vietnam where tank-on-tank battles seemed less likely if at all. While a solution was eventually found to make the combustion rounds usable in the thick of combat (by use of special ammunition covers removed before firing), the Sheridan was finally cleared for service in the bush. 3rd Squadron, 4th Cavalry and 1st Squadron, 11th Armored Cavalry Regiment were all equipped with Sheridans, replacing their collections of M113 armored personnel carriers (the 11th) and M48 Pattons (the 4th) in the process, and made ready for service in Vietnam in 1968. In January of 1969, no fewer than 54 Sheridans arrived in Vietnam, sans their complicated missile systems of course.
As the war progressed, Sheridans proved to have some misgivings during her stay in the theater. Her thin belly armor proved highly susceptible to enemy landmines, generally the method of warfare as selected by the North Vietnamese. As a consequence, Sheridan crews sometimes opted to sit atop their rides, completely exposed to small arms fire, than to be trapped inside of the Sheridans walls (this was also a matter of comfort, considering the humidity and heat of the region). It was not uncommon for crews to add additional bolt-on steel armoring along the underside of the hull, at the risk of covering up the escape hatch for the driver. The thick brush of Vietnam soon began taking their toll against the fragile Sheridans, leading up to a rise in maintenance and mechanical headaches. Many engines and drive trains were simply overworked when tackling what could be miles and miles of heavy thick brush. The dust of Vietnam was also quick to collect on the outer hull, eventually making its home within the various subsystems while mud proved a constant problem to suspension systems and tracks. M551's operated in conjunction with M113 armored personnel carriers in reconnaissance teams.
Along with land mine warfare, the Vietcong were also lethal with attacks using their Soviet RPGs (Rocket Propelled Grenades). Though primitive in concept, these man-portable systems launched an explosive rocket grenade at distance to defeat enemy armor. As the Sheridan was designed from the outset to be a light system, it was inherently thinly-armored by nature. This meant that the RPG's tank-killing properties could be used to good effect when needed. To make matters worse, the combustible projectiles stored within the Sheridan tank would more often than not lead to a complete Sheridan loss - unfortunately including crew. As such, Sheridan crews were quick to adapt rather simplistic fences made of chain link to help defeat such dangers - or at least deflate their lethal effects to an extent. This fencing was most often times added to the front hull via "homemade" supports, an area most likely to encounter such enemy attack. Storage space within the Sheridan also proved a premium and often led to crews stowing much of their gear, ammunition or other supplies (including fuel canisters, track links and cots) externally on either the turret bustle rack or on the flat hull rear atop the engine.
Seeing it that tank-versus-tank battles were not to be in Vietnam, the main gun fire power of the 152mm M81 system proved rather effective against most anything on the battlefield including fortifications - though the Sheridan's original sighting system offered little assistance to her gunners. The M625 Canister was particularly effective (it contained 10,000 flechettes!) for "cutting out" areas of dense thicket. Make no mistake about it - the M81 was a powerful gun when the situation called for it. Its massive recoil could easily jolt the system rearwards, lifting the front road wheels clear off the ground. In essence, the Sheridan was a Light Tank with the firepower of a Main Battle Tank. Similarly, the heavy caliber 12.7mm machine gun had the power to cut a man in half and take on light-armored vehicles as well. The tanks relatively small size made it ideal for concealment (particularly in areas of tall grass) when traveling or finding cover.
The Improved Sheridan
On April 22nd, 1971, 505 Hughes AN/VVG-1 laser range finders were purchased by the US Army to help improve the Sheridan sighting system when firing of the main gun. This effectively created a new Sheridan designation in the M551A1 to help distinguish this new form from her base one. Externally, these systems were further distinguished from previous production Sheridans by the laser designation system mounted just underneath the commander's 12.7mm machine gun. A new M127A1 telescope was also added as part of the sighting upgrade.
In all, some 200 M551 Sheridans made their way to Vietnam. Ironically, the amphibious capabilities were rarely used in the thick jungle setting. Nevertheless, its contributions to the conflict are what most people remember of the Sheridan legacy.
The Sheridan, Post-War
With the Vietnam War over for some years by this time, the Sheridan was due for some modernization. In 1977, she had her reliability improved through the implementation of a revised drive sprocket and engine block. Her smoke grenade launchers were now fitted in quadruple mountings, four to a turret side, as opposed to the original's single-file arrangement. Her throttle was reworked and her original co-axial 7.62mm machine gun was replaced by the standard M240 general purpose machine gun system. In all, these changes addressed some issues of the vehicle as encountered in Vietnam and made for a marked improvement in performance (albeit slightly heavier than the original Sheridan), no doubt extending her usefulness.
Operation Just Cause
In America's bid to depose Panamanian dictator Manuel Noriega in Operation Just Cause in December of 1989, the Sheridan was called into action once again - her first since the days of the Vietnam War. In the ensuing action, four Sheridans were covertly airlifted into the country and these were later joined by eight more (the eight were actually from a group of 10 air-dropped Sheridans - two being lost in the drops, the first was salvageable while the second purposely blown up with irreparable damage). Incidentally, these air-dropped Sheridans garnered Charlie Company, 3/73rd Armor a spot in armored warfare history when they became the first tanks to be "dropped" into a combat zone on December 20th, 1989. Their landing took place at Torrijos-Tocumen International Airport. Once again, the main guns proved highly effective in silencing the defenses and blockades of the Panamanian Army. These Sheridans also showcased their new smoke grenade discharger arrangement and were fitted with the M60A3 Tank Thermal Sight (TTS), assisting the gunners aim substantially over original Sheridans. Sheridans with the TTS system were further designated as M551A1(TTS) to differentiate the improvement.
The M551 was revered in her actions during Operation Just Cause, in particular by her lethal 152mm main gun. The Sheridan proved a versatile mount and its relatively compact size ensured that it could go where larger tank systems were restricted. In many ways, the limitations as seen in the image of a Sheridan trudging through foreign territory in Vietnam were gradually undone by the Sheridan in Panama. The M551 proved a vital and flexible implement in the opening rounds of the action and impressed warplanners and commanders alike thanks to her versatility and firepower.
The 82nd Airborne Embraces the Sheridan
While most other frontline units stopped operational use of Sheridans as the decades rolled on, the 82nd Airborne Division stayed true to their mount. Most importantly, the tank was still an air droppable resource that worked well within the confines of an airborne unit - the only such system in the US Army inventory (even to this day, though the Sheridan is no longer in active service). It could (relatively) easily fit inside of the cargo bay of a Lockheed C-130 Hercules and be air-dropped to waiting airborne personnel on the ground, adding immediate fire support to advancing infantry squads.
Operation Desert Shield
M551 Sheridans were deployed to ally Saudi Arabia in 1990 for Operation Desert Storm, a massive coalition build-up of force enacted to remove Saddam Hussein's army from their illegal take-over of Kuwait. In fact, Sheridans actually represented some of the earliest units to arrive in the theater, this accomplished through use of the massive Lockheed C-5 Galaxy transports (C-141 transports were also cleared for use by Sheridans by the way). While early arriving Sheridans still sported their European camouflage colors, they were eventually converted to a three-color "desert-friendly" pattern that was eons away from their olive shade used during the Vietnam days. When they needed to move intra-theater, the C-130 was ready to take the little machines airborne. By the end of the year, Sheridans in the Gulf were sporting the Shillelagh anti-tank missiles not brought to Vietnam in preparation for facing off against Hussein's impressive collection of armor. Driver stations were also improved by the inclusion of the same night vision system as found on the M2 Bradley carriers.
The Sheridans in the gulf - for the most part - retained their visual similarities to their Vietnam counterparts. Thanks to its actions in that previous conflict, the cupola shielding was now standard fare for crew protection. Improvements to the sighting system by this time were also a large step forward in the Sheridan's evolution. External stowage of essential and non-essential gear was still the norm. The fact that the system was also nearly a quarter of a century old was something special to note as well - considering the digital nature of the Gulf War to come, complete with stealth fighters, laser-guided bombs and heavy use of digital implements.
Beyond Sheridan
Apart from direct war participation, the Sheridan was utilized in Cold War exercises by American personnel in training. The National Training Center (NTC) at Fort Irwin, California made use of 300 such vehicles (designated as M551NTC). The fiberglass and plywood VisMod (Visually Modified) kits were an effort to alter the external appearance of Sheridans to mimic that of Soviet armor systems such as the BMP armored personnel series and the T-72 Main battle tank for use in specially-crafted war games. perhaps the most-closely associated use of the Sheridan in this fashion was in copying the look of the lethal four-barreled ZSU-23-4 anti-aircraft systems. While retaining their lower hulls, these Sheridans had a superstructure superimposed on their existing hulls and closely resembled their Soviet counterparts. After the end of the Cold War, actual Soviet equipment became readily available for use in such war games and these types of modifications were no longer needed.
Conclusion
Production of the M551 General Sheridan began in 1966 and ended in 1970 with totals topping a reported 1,562 systems. The Sheridan served actively from 1969 up until 1996 - quite a feat for any tank especially those with an origin dating back to the 1960s.
The Sheridan was evaluated by a number of American-friendly potential nations in its life but none of these ever secured any production orders. The Sherman and her legacy, therefore, were "all-American" from beginning to end. The Sheridan was stationed in South Korea with deterrent forces on watch and, similarly, in Europe. Sheridan crews trained extensively in Germany for the seemingly inevitable World War 3 scenario. How the Sheridan would have fared in such an all-out war against the cream of the Soviet crop is left to the imagination, though the system itself was developed indeed for such a war.
As it stands and despite her not in active service with the US Army, the M551 Sheridan has yet to be directly replaced in the Army inventory by a capable like-system.
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