The Pershing was the first operational heavy tank
of the US Army. It was designated a heavy tank when it was designed in
WWII due to its 90mm gun, which was at the time the largest caliber gun
found on a US tank. In 1957, the US developed the M103 tank which had an
even larger 120mm gun, and the M26 Pershing was re-designated as a
medium tank. The tank is named after General John J. Pershing who led the American Expeditionary Force in Europe in World War I, it was briefly used both in World War II and in the Korean War.
Intended as an improvement of the M4 Sherman,
the prolonged time of development meant only a small number saw combat
in the European theater, most notably the 9th Armored Division's
dramatic dash to take the Bridge at Remagen. In combat it was, unlike the M4 Sherman, fairly equal in firepower and protection to both the Tiger I and Panther tanks but was underpowered and mechanically unreliable.
This became even more evident in the Korean War, where the M26, while an overmatch for the T-34-85, had severe problems with the hilly terrain and was withdrawn in 1951 in favor of its improved derivative, the M46 Patton, which had a more powerful and reliable engine. The lineage of the M26 continued with the M47 Patton, and was reflected in the new designs of the later M48 Patton and M60 Combat Tank.