The M26 Pershing is a heavy tank, later designated as a medium tank, formerly used by the United States Army during the early years of the Cold War. It was used in the last months of World War II during the Invasion of Germany and extensively during the Korean War. The tank was named after General of the Armies John J. Pershing, who led the American Expeditionary Force in Europe during World War I.

The M26 was intended as a replacement of the M4 Sherman, but a prolonged development period meant that only a small number saw combat in Europe. Based on the criteria of firepower, mobility, and protection, US historian R. P. Hunnicutt ranked the Pershing behind the German Tiger II heavy tank, but ahead of the Tiger I heavy and Panther medium tanks. It was withdrawn in 1951 in favor of its improved derivative, the M46 Patton, which had a more powerful and reliable engine and advanced suspension. The lineage of the M26 continued with the M47 Patton, and was reflected in the new designs of the later M48 Patton and M60 tank.^{[citation needed]}

The M26 was the culmination of a series of medium tank prototypes that began with the T20 in 1942, and it was a significant design departure from the previous line of U.S. Army tanks that had ended with the M4 Sherman. Several design features were tested in the prototypes. Some of these were experimental dead-ends, but many became permanent characteristics of subsequent U.S. Army tanks. This series of prototype vehicles began as a medium tank project that was similar to, but more modern than the recently introduced M4 Sherman, and ended several years later as the U.S. Army's first operational heavy tank.

The U.S. Army's first lineage of tanks evolved from the M1 Combat Car and progressed to the M2 Light Tank, M2 Medium Tank, M3 Lee, and finally the M4 Sherman. These tanks all had rear-mounted Continental air-cooled radial aircraft engines and a front sprocket drive. This layout required a driveshaft to pass under the turret, which increased the overall height of the tank, a characteristic shared with German tanks of World War II that also used this layout. The large diameter of the radial engines in M4 tanks added to the hull height. These features accounted for the high silhouette and large side sponsons that were characteristic of the M4 lineage.

In the spring of 1942, as the M4 Sherman was entering production, U.S. Army Ordnance began work on a follow-up tank. The T20 tank reached a mock-up stage in May 1942, and was intended as an improved medium tank to follow the M4. An earlier heavy tank, the M6, had been standardized in February 1942, but proved to be a failure. The U.S. Army had no doctrinal use for a heavy tank at the time.

The T20 was designed to have a more compact hull than the M4. The Ford GAN V-8, a lower silhouette version of the GAA engine used in later variants of the M4, had become available. The engine had originally been an effort by Ford to produce a V-12 liquid-cooled aircraft engine patterned after the Rolls-Royce Merlin, but failed to earn any aircraft orders and so was adapted as a V-8 for use in tanks; use of this lower profile engine together with the choice of a rear transmission and rear sprocket drive layout made it possible to lower the hull silhouette and eliminate the side sponsons.

The T20 was fitted with the new 76 mm M1A1 gun, the 3-inch M7 was considered too heavy at about 1,990 lb (900 kg). New stronger steels were used to create a weapon weighing about 1,200 lb (540 kg). The 3 inch front hull armor was .5 in (13 mm) thicker than the 63 mm (2.5 in) front armor of the M4. The glacis plate slope was similar at 46°. The T20's overall weight was approximately the same as the M4.

The T20 used an early version of the horizontal volute spring suspension (HVSS), another improvement compared to the less robust vertical volute spring suspension (VVSS) of the early versions of the M4. Later prototypes of the M26 tested a torsion bar suspension, which became the standard for future U.S. tank suspension systems.