M4 Sherman Tank and M18 Hellcat Tank 

US Army Heritage and Education Center

HISTORIC OVERVIEW

Historic M4 Sherman TankThe M4 Sherman tank was the primary tank used by the United States and its Allies during the Second World War. During the war, over 50,000 were built and it chassis served as a model for thousands of additional vehicles. The M4 had a crew of four to five and was armed with a 75mm gun, a .50 caliber machine gun and two .30 caliber Browning machine guns. The M4's nickname came from the British practice of naming their American-built tanks after American Civil War generals. In this case, they chose Union General William Tecumseh Sherman. Unfortunately for the Allies, the Sherman was no match for their German counterparts in armament and armor. In response to these inadequacies, the US designed and built the M18 Hellcat.

 

The M18, built by Buick, boasted a larger 76 mm gun and an incredible top speed of close to 55 miles per hour. It was manned by four to five soldiers in an open-topped turret and fired high velocity armor piercing shells. Because of its speed and overall firepower, it was nicknamed the Hellcat. Also, because of its large gun, it was classified as a tank destroyer. Though it, too, had a number of initial failings in comparison to German armor, most were remedied quickly and the Hellcat became more than valuable in the European and Pacific theaters of World War II.

 

PRE-TREATMENT CONDITION

Before Treatment: Deteriorating WaxThe M4 Sherman and the M18 Hellcat tanks are exhibited outdoors on the "Trail of History" at the Army Heritage and Education Center in Carlisle, Pennsylvania. B.R. Howard & Associates, Inc. is currently under contract with AHEC to provide conservation treatment and maintenance of their collections on an as- needed basis. As part of this contract, AHEC curatorial/conservation staff scheduled the annual maintenance of the artifacts displayed on the "Trail of History" and requested condition assessments of both vehicles and recommendations for future treatment options. The tanks were found to have areas or components which were actively deteriorating due to exposure to constant temperature fluctuation and surface wetting. In addition, the M4 was subjected to air borne road salts from adjacent highways during the winter months. As a result, areas of paint loss and active corrosion were found to be concerns for both tanks. Precipitation entering the vehicles through engine grate covers and around the perimeters of the hatch covers caused continual high levels of humidity in the tank interiors, accelerating corrosion and paint loss. It should be noted that both tanks had been restored and made fully operational prior to their acquisition by the Army Heritage and Education Center; fuel and batteries had been remove but all lubricants and coolant remained in the mechanicals of each tank. Current finishes, painted stencils, and markings are not original to the period of historic use and it appears that little, if any, original paint or unit designation remain on the tank exteriors.

 

TREATMENT

Before Treatment: Corrosive ElementsThe treatments of the Sherman and the M18 Hellcat were nearly identical, focusing upon cleaning and maintenance of the exterior finishes and the mothballing of the tanks' mechanicals. The tanks were washed using a dilute anionic detergent solution in potable water. After cleaning, the tanks were rinsed with potable water and allowed to dry. The vehicles had been waxed by AHEC staff during previous maintenance cycles that had since deteriorated creating an uneven white haze on the flat Olive Drab paint. The deteriorated layer of wax was reduced using several applications of mineral spirits applied using soft cotton cloths. New applications of unbleached microcrystalline wax were then applied in multiple coats to ensure proper coverage. The gun barrels were then cleaned to remove all loose debris using nylon brushes attached to threaded fiberglass rods. Silica gel desiccant packs produced by AHEC museum personnel were then inserted into the barrels and neoprene tampions fabricated by B.R. Howard & Associates were installed at both the breech and muzzle openings, effectively sealing the gun tubes. All exterior openings were then sealed using minimally invasive and reversible materials. Loose components such as periscopes inserts and interior hatch rings were secured in their original locations. The engine compartments and mechanical components were also treated in similar manner for both tanks. Samples coolant was removed and tested; if necessary, the existing coolant was partially drained and the levels were again filled with a proprietary polyethylene glycol and retested to insure protection to 25 degrees below zero F. The engine oil was then drained and transported to an oil recycling center. The engine blocks were then filled to their maximum capacity using a non-detergent 30 weight motor oil. The shielded spark plugs were removed, cleaned, and a non-detergent 50 weight oil was injected into each of the engine cylinders and the sparkplugs were reinstalled. Oil and coolants were left in the engine blocks to minimize the possibility of internal corrosion developing given their long-term exhibition outdoor; typically museum vehicles exhibited inside would have all fluids and most lubricants drained and sealed. The engines were manually rotated to move the lubricants though the engine blocks. Engine and exhaust openings were sealed using reversible materials and minimally invasive procedures to limit moisture, insects, and rodents from entering the engine blocks. Recommendations for future maintenance were developed and presented to AHEC staff for consideration.

 


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