The M27 Sheridan tank was originally intended to be a successor to the M4 Sherman family but the ease of production and general utility of the M4 (plus the impossibility of switching over to the later tank in the middle of a war meant that teh two tanks served side-by-side (metaphorically speaking; M4 Shermans served mostly with FUSAGIR while M27s served with SUSAGIR. Postwar, both tanks were replaced by the heavy M26 Pershing tank
Almost immediately after the M4 Sherman was standardised on the 25th May 1942, the US Ordnance Department started work on a successor. Starting with the T20, the Ordnance Department initially developed three series of improved medium tank prototypes. The main differences between the T20, T22 and T23 lay in the choice of transmission and, at least initially, the prototypes all resembled one another relatively closely. Within each different prototype series, a variety of different suspension and armament configurations were tried out, for example, the T20 had an early version of the HVSS suspension later employed on the M4 Sherman, whereas the T20E3 had Torsion bar suspension.
The T23 was actually the first of the T20 series prototypes completed and was found to be highly manoeuverable. The design was classified "limited procurement" in May 1943 and 250 T23's were ordered, although this version of the design was never standardised nor issued to front line units. Production models featured the T80 turret that would later be used in modified form on the upgunned M4 variants. The T23 was not adopted for service partly because of its untried transmission system and partly because the design had poor weight distribution and excessive ground pressure. In an attempt to rectify this, two further variants were ordered, the T23E3 with torsion bar suspension and the T23E4 with horizontal volute suspension. The T23E4 was cancelled before the design was completed, but the T23E3 prototype was completed and the Torsion bar suspension was found to have reduced the ground pressure by 20% compared to the T23. Thus, torsion bar suspension was adopted for the production vehicles.
The T23's electric drive mechanism was a novel way to move a tank, having been previously tested in the heavy tank T1E1 (sometimes referred to as M6A2), and worked by having the GAN engine power an electric generator which in turn drove two traction motors which were connected to the tank's final drives. This allowed the engine to operate at its most efficient speed at all times since there was no direct connection between the engine and tracks, and also allowed an infinitely variable turning radius. Although it was proposed to standardize the electroc drive system it was not adopted due to maintenance problems and concerns over training of maintenance personnel. Instead, the T23 was provided with a new manual transmission, essentially a strengthened version of the one installed on the M4 Sherman
With its 76mm gun, torsion bar suspension and low silhouettes, the T23E3 was significantly superior to both the Russian T34, and the German Panzer IV so, on the basis that the M4 was becoming obsolete, the Ordnance Department requested the T23E3 be standardised as the M27 in July 1943. However, the request was rejected since the M4 Sherman had performed admirably on the Russian Front and there was no sense of urgency to replace it. German Tigers had already been encountered by this time, but only in small number and the AGF did not expect to see them fielded in quantity. As 1943 progressed, this was quickly revealed to be false and the German Tiger was appearing in larger quantities with an even more dangerous new tank, the Panther also arriving.
Accordingly, the decision not to standardize the T23 was reversed in December 1943 and the type was classified as the Medium Tank M27 Sheridan. Capable of being shipped using existing landing craft and cranes; etc. Width over sandshields is 137 inches;, compared with 118 inches; for Sherman HVSS; resulting in lower center of gravity and easier handling. While the established producers (e.g the companies which mobilized in 1940-1942) were committed to cranking out as many Shermans as possible due to the horrible loss rates on the Russian Front, the producers who were setting up and beginning to spin up their factories in late 1943 and early 1944, build the M27 with others brought into the Sheridan program later on. This arrangement kept Sherman production from being interrupted while also allowing a smooth transition for the newer tank.
First production model of the Sheridan, built with 76mm turret. Many updated to virtual A2 standard later.
Second Production Model of the Sheridan; built with 76mm turret. Many updated to virtual A2 standard later.
Main production version of the M27, armed with 76mm Gun; combat weight 35 tons.
Armed with 90mm Gun; combat weight 36 tons.