The M26 was the culmination of a series of medium tank prototypes that began with the
T20 in 1942 and 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 become permanent characteristics of subsequent U.S. Army tanks.
 The prototype series began as a medium tank upgrade of the M4 Sherman and ended as the U.S. Army's first operational "heavy" tank.
Improving on the M4
The 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, developed from the 3 inch anti-aircraft gun. 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 would become the standard for future U.S. tank suspension systems.
T22 and T23
The T22 series reverted to the M4 transmission because of problems with the early
Torqmatic transmission used in the T20. The T22E1 tested an
autoloader for the main gun, and eliminated the loader's position with a small two-man turret.
T23 with production cast turret mounting 76 mm M1A1 gun. The T23 turret would be used for the 76-mm M4 Sherman. Note the vertical volute spring suspension.
Through much of 1943, there was little perceived need within the U.S. Army for a better tank than the 75 mm M4 Sherman, and so, lacking any insights from the rest of the army as to what was needed, the Ordnance Department next took a developmental detour into electrical transmissions with the T23 series.
electrical transmission was built by
General Electric, and had the engine driving a
generator that powered two
traction motors. The concept was similar to the drive system of the German "Porsche Tiger" (later rebuilt as the Ferdinand/
Elefant). It had performance advantages in rough or hilly terrain, where the system could better handle the rapid changes in torque requirements.
The electrical transmission T23 was championed by the Ordnance Department during this phase of development. After the initial prototypes were built in early 1943, an additional 250 T23 tanks were produced from January to December 1944. These were the first tanks in the U.S. Army with the 76 mm M1A1 gun to go into production.
 However, the T23 would have required that the army adopt an entirely separate line of training, repair, and maintenance, and so was rejected for combat operations.
The primary legacy of the T23 would thus be its production cast turret, which was designed from the outset to be interchangeable with the turret ring of the M4 Sherman. The T23 turret was used on all production versions of the 76 mm M4 Sherman as the original M4 75 mm turret was found to be too small to easily mount the 76 mm M1A1 gun. The first production 76 mm M4 with the T23 turret, the M4E6, was built in the summer of 1943.
T25 and T26
The T25 and T26 lines of tanks came into being in the midst of a heated internal debate within the U.S. Army in the mid-1943 to early 1944 over the need for tanks with greater firepower and armor. A
90 mm gun mounted in a massive new turret was installed in both series. The T26 series were given additional frontal hull armor, with the glacis plate increased to 4 in (10 cm). This increased the weight of the T26 series to over 40 short tons (36 t) and decreased their mobility and durability as the engine and powertrain were not improved to compensate for the weight gain.
The T26E3 was the production version of the T26E1 with a number of minor modifications made as the result of field testing. Following its introduction into combat, it was renamed the M26 in March 1945.
After the war
Post World War II, some 800 M26 tanks were upgraded with improved engines and transmissions and 90-mm gun and were redesignated as the
The M26 was introduced late into World War II and saw only a limited amount of combat. Tank historians, such as Richard P. Hunnicutt, George Forty and
Steven Zaloga, have generally agreed that the main cause of the delay in production of the M26 was opposition to the tank from the
Army Ground Forces, headed by General
 Zaloga in particular has identified several specific factors that led both to the delay of the M26 program and limited improvements in the firepower of the M4:
- 1. Tank destroyer doctrine
- McNair, who was an
artillery officer, had promulgated the "
tank destroyer doctrine" in the U.S. Army. In this doctrine, tanks were primarily for infantry support and exploitation of breakthroughs. Those tactics dictated that enemy tanks were to be engaged by tank destroyer forces, which were composed of lightly armored but relatively fast vehicles carrying more powerful anti-tank guns, as well as towed versions of these anti-tank guns. Under the tank destroyer doctrine, emphasis was placed only on improving the firepower of the tank destroyers, as there was a strong bias against developing a heavy tank to take on enemy tanks. This also limited improvements in the firepower of the
 The US Army Ground Forces that supported this doctrine got the approval of new TD projects,
one of them using the same 90 mm gun, while at the same time they were blocking tank projects.
- 2. Simplification of supply
- McNair established "battle need" criteria for acquisition of weapons in order to make best use of America's 3,000-mile-long (4,800 km) supply line to Europe by preventing the introduction of weapons that would prove unnecessary, extravagant or unreliable on the battlefield. In his view, the introduction of a new heavy tank had problems in terms of transportation, supply, service, and reliability, and was not necessary in 1943 or early 1944. Tank development took time, and so the sudden appearance of a new tank threat could not be met quickly enough under such criteria.
- 3. Complacency
- A sense of complacency fell upon those in charge of developing tanks in the U.S. Army because the M4 Sherman, in 1942, was considered by the Americans to be superior to the most common German tanks: the
Panzer III and early models of the
Panzer IV. Even through most of 1943, the 75-mm M4 Sherman was adequate against the majority of German armor, although the widespread appearance of the German
7.5 cm KwK 40 tank gun during this time had led to a growing awareness that the M4 was becoming outgunned. There was insufficient Intelligence data processing and forward thinking to understand that there was an ongoing arms race in tanks and that the U.S. needed to anticipate future German tank threats. The
Tiger I and
Panther tanks that appeared in 1943 were seen in only very limited numbers by U.S. forces and hence were not considered as major threats.
 The end result was that, in 1943, the Ordnance Department lacking any guidance from the rest of the army, concentrated its efforts in tank development mainly on its major project, the electrical transmission T23.
 By contrast, the Russians and British were engaged in a continuous effort to improve tanks; in 1943, the British begin development of what became the 51-ton
Centurion tank (although this tank would reach service just too late to see combat in World War II) and, on the Eastern Front, a full-blown tank arms race was underway, with the Soviets responding to the German heavy tanks by starting development work on the
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. Ordnance favored the 76 mm gun, electrical transmission T23. Theater commanders generally favored a 76 mm gun medium tank such as the T23, and were against a heavy 90 mm gun tank. However, testing of the T23 at Fort Knox had demonstrated reliability problems in the electrical transmission of which most army commanders were unaware. The new 76 mm M1A1 gun approved for the
M4 Sherman seemed to address concerns about firepower against the German tanks. All participants in the debate were, however, unaware of the inadequacy of the 76 mm gun against the frontal armor of the
Panther tank, as they had not researched the effectiveness of this gun against the new German tanks, which had already been encountered in combat.
Single prototype of 90 mm gun T26 turret mounted on an M4A3 chassis.
Lesley J. McNair had agreed to the production of the 76 mm M4 Sherman, and he strongly opposed the additional production of the T26E1. In the fall of 1943, he wrote this letter to Devers, responding to the latter's advocacy of the T26E1:
The M4 tank, particularly the M4A3, has been widely hailed as the best tank on the battlefield today. There are indications that the enemy concurs in this view. Apparently, the M4 is an ideal combination of mobility, dependability, speed, protection, and firepower. Other than this particular request—which represents the British view—there has been no call from any theater for a 90 mm tank gun. There appears to be no fear on the part of our forces of the German Mark VI (Tiger) tank... There can be no basis for the T26 tank other than the conception of a tank versus tank duel—which is believed unsound and unnecessary. Both British and American battle experience has demonstrated that the antitank gun in suitable number and disposed properly is the master of the tank. Any attempt to armor and gun tanks so as to outmatch antitank guns is foredoomed to failure... There is no indication that the 76 mm antitank gun is inadequate against the German Mark VI (Tiger) tank.
General Devers pressed on with his advocacy for the T26, going over McNair's head to General George Marshall, and on 16 Dec 1943, Marshall overruled McNair and authorized the production of 250 T26E1 tanks. 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. Testing and production of the T26E1 proceeded slowly, however, and the T26E1 did not begin full production until November 1944. These production models were designated as the T26E3.
A single prototype of a T26 turret mounted on an M4A3 chassis was built by Chrysler in the summer of 1944, but did not progress into production.
Hunnicutt, researching Ordnance Department documents, asserts that Ordnance requested production of 500 each of the T23, T25E1, and T26E1 in October 1943. The AGF objected to the 90 mm gun of the tanks, whereas the Armored Force wanted the 90 mm gun mounted in a Sherman tank chassis. General Devers cabled from London a request for production of the T26E1. In January 1944, 250 T26E1s were authorized. General Barnes of Ordnance continued to press for production of 1,000 tanks.
According to Forty, Ordnance recommended that 1,500 of the T26E1 be built. The Armored Force recommended only 500. The AGF rejected the 90 mm version of the tank, and wanted it to be built with the 76 mm gun instead. Somehow, Ordnance managed to get production of the T26E1 started in November 1944. Forty primarily quoted from a post-war report from the Ordnance Dept.
Production finally began in November 1944. Ten T26E3 tanks were produced that month at the Fisher Tank Arsenal, 30 in December, 70 in January 1945, and 132 in February. The Detroit Tank Arsenal also started production in March 1945, and the combined output was 194 tanks for that month. Production continued through the end of the war, and over 2,000 were produced by the end of 1945.
The so-called "Super Pershing" before extra armor welded on. Note the 73
gun to compete with the 88 mm KwK 43 L/71 gun on the
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.
Post World War II
In May 1946, due to changing conceptions of the U.S. Army's tank needs, the M26 was reclassified as a
medium tank. Designed as a
heavy tank, the Pershing was a significant upgrade from the M4 Sherman in terms of firepower and protection. On the other hand, its mobility was unsatisfactory for a medium tank (it used the same engine that powered the M4A3, which was some ten tons lighter) and its transmission was somewhat unreliable. In 1948, the M26E2 version was developed with a new powerplant. Eventually, the new version was redesignated the
M46 General Patton and 1,160 M26s were rebuilt to this new standard. Thus the M26 became a base of the Patton tank series, which replaced it in early 1950s. The
M47 Patton was an M46 Patton with a new turret. The later
M48 Patton and
M60 Patton, which saw service in later Vietnam and Mideast conflicts and still serve in active duty in many nations today, were evolutionary redesigns of the original layout set down by the Pershing.