The T26E4 was a heavy tank armed with a high velocity gun to counter the firepower of the latest German heavy panzers. With the T26E3 Pershing ongoing for serial production, the Ordnance Department had authorized a diversion of 25 T26E3s from their original configuration to mount the latest anti-tank gun in development, the 90 mm T15 L/73 high velocity gun. The first temporary pilot of the vehicle, designated as Heavy Tank T26E4-1 “Super Pershing” was sent into combat in April 1945. Using the earlier T26E1 hull, extensive modifications to its fire control was required due to the turret being originally designed to mount the shorter 90 mm M3 L/53 cannon only.
A 90 mm T15E1 with single piece ammunition was hastily installed on the first temporary pilot T26E4-1. Because the gun proved to be too heavy for the tank’s size, the hull was heavily modified, requiring two large equilibrator springs mounted externally on top of the turret to control elevation of the gun. To balance the extremely heavy barrel on the front, a large counterweight was welded at the rear of the turret. Other modifications involved the installation of heavier elevation gear, turret traveling and turret ring locks, and the gun cradle. The second temporary pilot T26E4-2 retained all the modifications of the first temporary pilot, but had now used the hull of the T26E3 instead, and mounted a 90 mm T15E2 with separate piece ammunition.
As the T26 turret wasn’t clearly designed to adapt the 90 mm T15 gun, additional modifications were authorized for a proper production T26E4 by incorporating a hydropneumatic equilibrator mounted internally within the turret to replace the external spring equilibrator and rearranged ammo racks. This production version would later be applied to the remaining 23 T26E4s. However, as many modifications as there could be, the T26E4 turret remained the same as the T26E3 turret by design. It still couldn’t wield such a long-barreled cannon effectively without some reliability issues.