Knowing D-Day approached, and in order to assault fortifications, the US army looked to 'upgrade' the standard M4A3 Shermans.
 
The resultant tank arrived in the June–July 1944, with the US Army receiving a limited run of some 250 M4A3E2 Jumbo heavy assault tanks. Equipped with very thick (100mm) frontal armor (glacis plate), sloped at a steeper angle than normal to eliminate the hull bulges on the standard glacis, and a further 150mm of armour to the front of the turret. It was praised for being the only US tank able to survive a direct hit from a German 88. The 43 ton heavy assault tank arrived armed with the reliable 75mm gun in a new, heavier, T23-style turret.
 
As the Americans gained more bitter experience against the heavier armoured and better gunned German tanks the call went out to re-arm all the M4s to the 76mm, this project would eventually be canceled due to the many difficulties presented by the small turrets of the M4, the Jumbo however had the larger turret already, so in February 1945 Patton's third army was to refit in field workshops (adding the .50cal mount at the same time to replace the older .30cal). Eventually other armies followed suit and some 100 M4A3E2 were converted with the new 76mm.