When the M26 Pershing was developed, it was already recognized to be lacking in comparable firepower to the German counterparts, which had the long-barreled 88 mm KwK 43 cannon on the Tiger II tanks. The US attempted to remedy this issue with the 90 mm T15 cannon with the T26E4 tanks, but these were considered cumbersome due to their extremely large cartridges, hindering the reload process within the tank. Further development led to the 90 mm T54 cannon, which had comparable firepower to the T15 cannon, but with a smaller ammunition for easier reloading within the tank. This new gun was installed into a prototype designated M26E1, however the post-war environment in terms of budget cuts and lack of need to produce new tanks led to the project's discontinuation and none of the tanks were considered.

Introduced in Update 1.47 "Big Guns", the M26E1 has a very similar profile to the M26 aside from its very long L/73 90 mm Gun T54. However, this allows the M26 medium tank profile to have similar firepower to the T26E1-1 "Super Pershing" and T32 heavy tank to be able to compete against Rank IV vehicles at a faster reload rate. That said, the extra long barrel length compared to the hull can be a weak spot as enemies can snipe the tank barrel poking out of cover and disable the M26E1's firepower. The armour and mobility remains similar, if not the same, as the standard M26.

Originally an in-game premium vehicle purchasable with Golden Eagles, it has since been removed from in-game sale after the 9th Anniversary Sale.