A very early concept drawing for the new light tank, XM 551 from Cadillac. --R.P. Hunnicutt		Pilot # 3, hand built as the design continued to develop. Among other areas, they were testing a caliber .50 spotting rifle mounted above and to the left of the cannon. --R.P. Hunnicutt

"OK ... in folder twenty-two, marked Armored Reconnaissance / Airborne Assault Vehicle are the most recent designs that have the turret back in front of the mid point, engine and drive line to the rear and a four man crew. I don't care about the gun, someone else will throw that in ... I just need it to drive, float, fight and fly!!"

All things are possible to engineers and based on the design specifications, two groups were in competition for funding and further development of the light tank, Cadillac at Cleveland and a joint proposal from Aircraft Armaments & Allis Chalmers. Both companies had started with a blank sheet of paper and the designs were a radical departure from what tankers were familiar with. New materials and manufacturing techniques pioneered in the aircraft industry and opening stages of the space race held great promise.

AAI alone, also floated a plan for a remote controlled tank, that in a working design model, had "legs and feet" and could walk, swim and dig trenches". The Army further experimented with the design, added wheels and visualized it as a carrier for a recoilless rifle. The New York Times reported, "The vehicle's operator lies on his stomach and controls the engine, which is in the rear, as well as the transmission of power to the legs. He can turn the tank by braking the legs on one side or stopping the side entirely.". This project never progressed beyond the demonstration stage.
At the In Progress Review at the Detroit Tank Plant, the initial design from GM in Cleveland won the day and the money was granted. June 1960, the project was designated as the AR/AAV XM 551 and General Sheridan's name was designated the following year. The program was underway.

Sixteen months later, the Cleveland Press reported the contract had finally been signed for production and almost six million federal dollars were allocated to retool the Cadillac plant for Sheridan production. Even before the final designs were approved and the prototypes field tested, plans for production began in earnest. A work force in excess of 4000 personnel was visualized with at least two major production lines running at the plant, the M551 and the M114. If all went according to plan, tank production could begin in 1962. In the Fall of 1961, more good news, the plant received additional contracts for both 105mm and 155mm self propelled howitzers.

During this same period, a joint Sperry and Ford Aeronutronics program to add a guided missile component to the developmental 152 mm M81 cannon was also making design progress. It was designated as the Shillelagh system. The M81 had already become the lead choice for the XM 551 in the Army planning documents and the addition of a missile was seen as a great step forward in fighting capability. Other weapons choices had been considered but the 152 mm cannon firing a combustible case round offered the new technology and the new approach that seemed to best fit the Sheridan profile.

The M81 cannon has its own interesting story, although we have found only fragments. The idea of a "big bullet" 152 mm, combined with a missile launcher and combustible case ammunition clearly had a powerful lobby in the Army and manufacturers. In Europe, our allies and adversaries favored incremental improvements in tank gun ammunition based on faster burning, more powerful propellants, new designs in explosive and kinetic rounds and experiments with larger gun tube diameters, 90 mm, 105 mm, 120 mm. Only the US seriously pursued the large bore gun-launcher system. This cannon, tied to the Sheridan, the MBT 70 and the M60A2 would have a long and troubled history.

When the missile program showed signs of stalling in development, the decision was made to continue the Sheridan project based only on the M81 gun and conventional ammunition. If the missile later met developmental milestones, it could be reintegrated to the Sheridan program. Though the early 1960s, the first prototypes of the XM 551 were delivered to the Army for extensive testing. Designers then incorporated the lessons learned and tried to solve emerging problems on the ranges and test roads as well as the design studio. The program was clearly taking shape, the later prototypes very closely resemble the final approved design.

This is not to say, however, that the XM 551 was the only design iniative alive. Even as the money began to flow and the M81 cannon with combustible case ammunition programs merged with the light-airborne capable tank program, the Army sponsored a design contest to consider tank-like vehicles just beyond the capability of current manufacturing. Lockheed Aircraft engineers, Robert and John Forsyth, won the award with a radical design. The vehicle was articulated with two crew chambers, "... combining mobility with tactical self sufficiency. Three men including one trained in nuclear projectiles, would ride in the forward tractor unit, with four men including a ' tank support team ' riding in the rear one. They could fight either from the vehicle or dismounted." . The tank would feature a 155 mm cannon, a 20 mm cannon and a heavy machine gun, the New York Times reported. An interesting experiment that never rolled off the design board. In the real world, the Cleveland newspapers proudly tracked the growing payroll, employee count and significant contracts associated with the Tank Plant.

Congressman William E. Menshall, ( R-Cleveland ) in budget hearings in Washington in 1963, tried to determine the value of all actual and expected Army contacts related to the Cleveland Tank Plant. The total expected dollar amount was fixed at 363 million, including howitzers, the M114 and most notably the M551. With that much money at stake, the program was close to achieving unstoppable momentum. Also that year, as tooling continued on the M551 production line, the single shift of 3600 workers stopped for a brief ceremony; the 1000th M114 rolled off the line in July.

In Washington, the expanding Vietnam War, space race and "guns and butter" policies of the Johnson Administration led to huge funding commitments and to keep projects alive, the military was asked to review all new contacts and look for savings. In sub committee, the question was asked, "why is Chrysler running the Detroit Plant and building M60s and GM is getting ready to start production on tanks in Cleveland? Does it make more sense for Chrysler to take over all tank production?". In spite of existing contracts, the entire Sheridan program and administration of the Cleveland tank plant was put up for bid to drive the project cost down. Chrysler won and suddenly it seemed as though GM would surrender the keys to the building and the blueprints.

The news rocked Cleveland, particularly when GM announced that to fully operate the plant under their corporate structure would take upwards of a six month slow start program. The newspapers reported that almost 3000 workers would be laid off. Behind the scenes, GM was grandfathered into the production of the M109s and M114s. They would be sub-contractors to GM in the plant, the M551 would become a Chrysler program. Then, a few months later, the papers reported that just the opposite would occur, Chrysler would assume the GM projects in exchange for returning the Sheridan to GM. From union officials to local politicians, all of this was a hugely unwelcome annoyance.

The following year, the projects at the Cleveland Tank Plant were up for bid once more ... this time, GM won all existing contracts with the lowest bid and planned to control the entire plant and all production lines by mid 1965. The recently hired Chrysler workers became GM workers, the entire work force numbered just under 2000 employees. As the M114 line completed its final copy, the work force dramatically dropped to just over 700. Within one year, the vast majority of union employees at the plant had drawn their cards from one local, reported to new local and then gotten in line at the unemployment office.

In 1965, Sheridan prototype # 12 was delivered to the Army and it represented the final design that Cadillac and Cleveland Tank Plant felt matched all the Army requirements and could be readily produced at the factory. The same year, in an internal reorganization, GM moved a management team from their Allison transmission division into the plant to supervise all projects. The final M551 design included the "swim screens" that anyone involved with the vehicle up to 1978 will fondly recall. The water jet propulsion system was gone, the tracks would thrash at the water and create thrust.

Because the M551 had been a "blank sheet" project, almost all components had been specifically designed and hand built for the prototypes. Actual production required a vast support network of outside contractors and with Allison at the helm and production seemingly safe again with GM, mid 1965 saw hundreds of suppliers and sub contractors descend on Cleveland to attend production conferences. Plant Manager, Mr. E. D. Solms, a life long GM executive, valued the total dollar amount of sub contact work at 70 million for the life of the project. With the optimism of an American manufacturer, a businessman and a GM employee, he predicted that the M551 could serve as the base for an entire family of US Army vehicles and that they all would be built in Cleveland. No government money was used for these "side projects", GM financed the additional designs. The call went back to the union halls, assembly-fabrication workers of all skills and trades needed at the tank plant. The M551 was the major production line, running in another wing of the massive factory was the M109 howitzer line.

Pilot # 9 in the design series, this is almost the final design that was authorized for full production. Note the bore evacuator sleeve, the CBSS was not yet under development. Also, by now, the water propulsion system had been eliminated. --R.P. Hunnicutt		The surf board is in the fording position and the swim screens, stored in chambers running along the upper edges of the hull, are fitted together. It wasn't pretty but it met the Army requirements. --R.P. Hunnicutt

Actual production at a slow rate began in 1966 and on 29 June, the first production model rolled off the assemble line to much applause. General Frank S. Besson Jr., commander of the US Army Materials Command was the noted guest and he remarked,

"This tank is a major addition to our military ' bag of tracks'. The General Sheridan represents the first weapons system of major significance to be developed and produced by the Army Material Command under the project management concept since reorganization of the Army in 1962."

The final Sheridan was produced at the Cleveland Tank Plant in 1970. A total of 1662 were built. All of the key design criteria had been met, it was light and could be deployed by parachute. The 152 mm cannon with missile launcher could defeat any Soviet tank. It was small but retained a four man crew, it was fast, 35 mph was possible with a full combat load. The automotive platform offered a wide variety of other possible uses and ... at about 3 mph ... it could swim.

As the vehicle went into production, staff officers created elaborate scenarios for its use. Not unlike Star Wars twenty years later, before there was a fully operational system, there were glowing reports featuring great art in much of the popular press. However, at the highest levels of the Army, many senior officers were not impressed. The program had funding and momentum but there was a lobby behind the scenes at the Pentagon that opposed the fielding of the M551. At a minimum, they wanted a very slow and controlled start up.

A mid production run Sheridan as it looked for a publicity still. The CBSS is installed so the bore evacuator sleeve is gone. Also, the metal shields surrounding the TC position are now standard. These photos represent a very small percentage of images available in the R.P. Hunnicutt book. If you have any interest in the fully detailed story of the Sheridan or other light tank development initiatives in the US, please order your copy now. --R.P. Hunnicutt

There were many roll out problems with the system and these were identified and corrected during the life of the production run. Modification teams were created to chase down the fielded tanks while the production line maintained a slow pace to adapt to changes as they arose. The new main gun required much fine tuning and only at vehicle #700 did the Closed Breech Scavenging System, designed to clear the cannon of any burning residue from the combustible ammunition, become a standard item. If at a museum, you find a Sheridan with gun tube fitted with a standard bore evacuator sleeve, it is an early production model. The sleeves were left on even as the CBBS was added.

Eaglehorse troopers in Germany will recall the laser range finder on this tank; these were added well after the production line was finished. Troopers from the Vietnam era may not recall much about the missile launching system. Those vehicles sent to Southeast Asia deployed without that component.

For the designers at the tank plant, watching the slow but steady production in the massive factory must have given them a sense of distinct pride. Years of hard work, politics and industrial competition had finally led to the first tanks rolling off the assemble line. There was, however, one remaining problem, the field modification team never had to travel very far. As the final inspection was finished for each tank by a joint team of military and civilian technicians and it was declared ready to ship, the driver carefully drove it to a secure lot next to the factory and parked the band new Sheridan. In late 1968, against any potential ground attack, Cleveland was the most heavily defended city in the United States. At the tank plant, over 1500 M551s sat hub to hub in the snow.