The tank was named after General of the Armies John J. Pershing, who led the American Expeditionary Force in Europe during World War I.

In February 1945, the T26 was fielded in the European Theater, where its performance received early praise from Army Ordnance officials.

From mid-1943 to mid-1944, development of the 90 mm up-armored T26 prototype continued to proceed slowly due to disagreements within the U.S. Army about its future tank needs.

The accounts of what exactly happened during this time vary by historian, but all agree that Army Ground Forces was the main source of resistance that delayed production of the T26.

In September–October 1943, a series of discussions occurred over the issue of beginning production of the T26E1, which was advocated by the head of the Armored Force, General Jacob Devers.

However, testing of the T23 at Fort Knox had demonstrated reliability problems in the electrical transmission of which most army commanders were unaware.

Although it could reliably penetrate the frontal armor of a Tiger 1 at standard ranges, all participants in the debate were, however, unaware of the inadequacy of the 76 mm gun against the frontal armor of the Panther tank, specifically its upper glacis (although its turret could still be penetrated at standard ranges), as they had not researched the effectiveness of this gun against the new German tanks, which had already been encountered in combat.

Both British and American battle experience has demonstrated that the antitank gun in suitable number and disposed properly is the master of the tank.

Then, in late December 1943, Devers was transferred to the Mediterranean, where he eventually led the invasion of Southern France with the 6th Army Group.

In his absence, further attempts were made to derail the T26 program, but continued support from Generals Marshall and Eisenhower kept the production order alive.

Firing trials with the T15E1 revealed that the length and weight of the single-piece ammunition made it difficult to stow inside the tank and load into the gun.

[citation needed] Designed as a heavy tank,[nb 2] the Pershing was a significant upgrade from the M4 Sherman in terms of firepower, protection, and mobility.

The later M48 Patton and M60, which the former saw service later in the Vietnam War and both saw combat in various conflicts in the Middle East and still serve in active duty in many nations today, were evolutionary redesigns of the original layout set down by the Pershing.

Development of the M26 during World War II was prolonged by a number of factors, the most important being opposition to the tank from Army Ground Forces.

[42] Due to the repeated design and production delays, only 20 Pershing tanks were introduced into the European theater of operations before the Battle of the Bulge.

[44] In February 1945, Major General Gladeon M. Barnes, chief of the Research and Development Section of Army Ordnance, personally led a special team to the European Theater, called the Zebra Mission.

Clarence Smoyer: We were told to just move into the intersection far enough to fire into the side of the enemy tank, which had its gun facing up the other street [where the Sherman had been destroyed].

When I turned our turret, I was looking into the Panther's gun tube; so instead of stopping to fire, our driver drove into the middle of the intersection so we wouldn't be a sitting target.

[50][51] On the same day, another T26E3 was knocked out in the town of Niehl near Cologne, by a rarely-seen Nashorn 88 mm tank destroyer, at a range of under 300 yd (270 m).

[53] The T26E3s with the 9th Armored Division saw action in fighting around the Roer River with one Pershing disabled by two hits from a German 150 mm field gun.

[43] A platoon of five M26s, less one that was being serviced, played a key role in helping Combat Command B of the 9th Armored capture the Ludendorff Bridge during the Battle of Remagen on 7–8 March 1945, providing fire support to the infantry in order to take the bridgehead before the Germans could blow it up.

The turret had 80 mm thick rolled homogeneous armor (RHA) from a Panther upper glacis welded to the mantlet, covering the front.

However, while defending Jinju on 31 July, all of these tanks experienced engine overheating and became immobilized due to insufficient maintenance on belts and cooling fans, and eventually all of them were self-destructed.

[63] The 70th Tank Battalion at Fort Knox Kentucky had pulled World War II memorial M26s off of pedestals and reconditioned them for use, but had to fill out two companies with M4A3s.

The 1st Marine Division at Camp Pendleton California had all M4A3 howitzer tanks, which were replaced with M26s just days before boarding ships for Korea.

Although it had better anti-tank capability than the M4A3E8 thanks to its 90 mm gun, its underpowered engine which wasn't well suited to Korea's mountainous terrain, and its tendency to overheat quickly made it less liked among crews, and most were thus temporarily withdrawn in favor of the more reliable "Easy Eight" Sherman.

[69] With the marked decrease in tank-to-tank actions, the automotive deficiencies of the M26 in the mountainous Korean terrain became more of a liability, so some M26s were withdrawn from Korea during 1951 and replaced with M4A3 Shermans and M46 Pattons.

[75] While M26 Pershings disappeared from Korea during 1951, tank units deploying to West Germany were equipped with them,[76][77] until replaced with M47 Pattons during 1952–53.

[80] In 1952, the Belgian Army received 423 M26 and M26A1 Pershings, leased free of charge as part of a Mutual Defense Assistance Program, then the official designation of U.S. military aid to its allies.

However, in the spring of 1953, M26s for three months equipped the 1st Heavy Tank Battalion of the 1st Infantry Division, an active unit, before they were replaced by M47s.