Prior to the invasion of Europe, combat experience in North Africa and the Mediterranean had shown the weakness in the thin armor of the M4 Sherman. With progress on the T-14 assault tank going nowhere, it was decided to up-armor a standard late model 75mm M4A3 Sherman. This tank, nicknamed "Jumbo", was classified as the M4A3E2.Starting in May 1944, Fisher Tank Arsenal had modified 254 vehicles to this configuration by July 1944. These modifications included adding 1.5 inches of armor plate to the glacis and upper hull sides. This increased the front from 2.5 inches to 4 inches and the sides from 1.5 inches to 3 inches. The differential housing was also replaced with a casting of 5.5 inches, increasing the thickness by 1.25 inches. Except for a minor alteration to the transmission, the deletion of the lights and siren, and taller gun travel lock mounts, these were the only modifications to the hull.
The turret, however, was a completely new design. It closely resembled the T-23 turret used on later model M4s equipped with the 76mm gun. In fact, this turret used the same 3.5-inch M62 gun mount (with an additional block of 3.5-inch armor welded to the front) as the 76mm T-23 turret. Initially, all tanks were armed with the 75mm gun M3 with the belief that the 75mm gun fired a better high explosive round than the 76mm gun M1A1. The cast turret sidewalls and rear consisted of 6-inch armor with a 1-inch rolled plate for the roof welded to this, leaving a prominent weld bead.
As stated earlier, all the original tanks were armed with the 75mm gun M3. In March 1945, the U. S. Army issued orders approving the installation of the 76mm gun M1A1. However, it is my belief that this modification was done at field level even earlier. As the mantlet and trunnions were virtually identical to the 76mm guns, it only required a slight adjustment for installation. I have seen photos in February 1945 of "Jumbos" with 76mm guns. It also appears that of the 76mm-gunned tanks, about 50 percent were armed with the 76mm M1A1 and the other half with the M1A2 gun with threaded muzzle brake caps.
Since the overall tank weight increased from 34.8 tons to 42 tons, all "Jumbos" were permanently fitted with extended end connectors, commonly referred to as duckbills. Fuel economy stayed the same with a range of about 100 miles, but speed decreased by 4 mph to 22 mph.
All "Jumbos" were used exclusively in Northwest Europe from July 1944 until the Armistice in May 1945.
