T26E4 Super Pershing

The so-called "Super Pershing" before extra armor welded on. Note the 73 caliber gun to compete with the 88 mm KwK 43 L/71 gun on the King Tiger.
The 90mm M3 gun of the Pershing was similar to the German 88 mm KwK 36 used on the Tiger I. In an effort to match the firepower of the King Tiger's more powerful 88 mm KwK 43, the T15E1 90 mm gun was developed and mounted in a T26E1 in January 1945. This tank was designated T26E1-1. The T15E1 gun was 73 calibers in length and had a much longer high-capacity chamber. This gave it a muzzle velocity of 3,750 ft/s (1,140 m/s) with the T30E16 APCR shot and could penetrate the Panther's frontal armor at up to 2,600 yd (2,400 m). The model shown used single-piece 50-inch-long (1,300 mm) ammunition and was the only Super Pershing sent to Europe.

A second pilot tank was converted from a T26E3 and used a modified T15E2 gun that had two-piece ammunition. Twenty-five production models of the tank, designated T26E4, were built. An improved mounting removed the need for stabilizer springs.

Post-war, two M26 tanks had the T54 gun installed, which had the same long gun barrel, but the ammunition cartridge was designed to be shorter and fatter, while still retaining the propellant force of the original round. The tanks were designated as the M26E1 tank, but lack of funds cut off further production.