Thursday 14 August 2014

History of the Pershing: T20 to M26

I've posted about American T20 series tanks before, but not in significant detail. This article will go into much more detail about the T20 tank and its descendants that ultimately resulted in the M26 Pershing tank. Since the supplier of these documents did not wish for them to be reproduced fully, this article series will only contain photographs from the scanned documents.

While the Ordnance Department was working on Sherman tanks armed with a 76 mm gun and a 105 mm howitzer, another project was underway to produce an entirely new medium tank. The new tank would have the same engine, transmission, and suspension as the Sherman, but a lower silhouette and a turret mounting a 76 mm gun. The next step in the project would be an upgrade to a 90 mm gun and use an improved electric transmission. In parallel, a heavier design that also mounted the 90 mm gun was being developed. This project, approved on May 25th, 1942, resulted in the T20, T23, T25, and T26 tanks.

The Army did not appreciate the results of the program. On September 13th, 1943, the Chief of Ordnance recommended that 500 T23 tanks be produced, 500 T25 tanks, 500 T26 tanks, and 500 T71 GMCs (an M10 tank destroyer with a 90 mm gun). The Commanding General of the Army Service Forces declined this recommendation on October 4th. A T23 with a 90 mm gun was built and shown to various high ranking officers, but the army was "not in favour of the 90-mm gun" as there was never a specific request for this gun, nor did it fit into the 30-ton weight limit. 250 T23 tanks armed with 76 mm guns, as well as 40 T25s and 10 T26es were approved on June 3rd, 1943. Development of these tanks progressed well enough for 500 additional units of each type to be requested in September, but the Director of the Requirements Division advised that "the proposal to build these additional quantities was not favourably considered at this time". However, when the Ordnance Department repeated the request in December of 1943, they were given permission to produce 250 additional T26 tanks (260 in total).

The electric transmission was deemed too heavy during the design process, and replaced with a Torqmatic in the two heavier designs, resulting in the T25E1 and T26E1 tanks.

The first T26E1 was completed by Fisher Tank Division, and arrived at Aberdeen on March 6th, 1944. A demonstration was held on March 30th, with the Secretary of War, Chief of Staff, and other high ranking military members present. The demonstration was impressive enough that "this new tank, which is superior to all known tanks" was approved for large scale production. At this point, the tank is described as having "...three speed Torqmatic transmission to increase the mobility of the vehicle and decrease driver fatigue, and a torsion bar suspension and 24-in. center-guide track to increase maneuverability and dependability in the field. The tracks were driven by the rear sprocket. Power was supplied by a 500-hp Ford GAF engine. Thicker armour was used for added protection, thicknesses of up to 4 1/2 in. on the turret front being used. One of the outstanding features of the vehicle was the use of the 90-mm Gun M3, which fired a 24-pound projectile capable of piercing a 4-in. armor plate at 2,000 yards."

Another demonstration was held in April of 1944, showing the T25E1 and T26E1 to the Secretary of War, Undersecretary of War, and Generals Marshall, McNair, McNarney, Porter, Weldron, Clay, Maxwell, Somervell, and Styer.

The tanks continued trials at Aberdeen until May 21st, 1944, racking up 1593 miles on the first pilot vehicle and 569 on the second. The overall design of the vehicle was considered sound, and the transmission, suspension, and gun were satisfactory. However, there were problems with cooling the engine and differential, oil leaks, repeated failure of the connection between the engine and flywheel, and the ammunition rack was deemed unsatisfactory. The vehicle was also found to be very wide. It was only possible to use the 60-ton Bailey bridge (among many others, the photograph of crossing a Bailey bridge is missing from the document) if the curb was removed, or protected with timber. Aberdeen gave the recommendation to put the tank into production, provided that the aforementioned defects were corrected.

T26E1 crossing the Trestle Bridge. A scribble across the medium classification indicates that this photo was archived not long before the classification changed.

Efforts to correct the defects were made from May 22nd to September 10th, by which point the first vehicle accumulated 4025 miles and the second 1805 miles. A new Ford V-8 engine operated satisfactorily for 1500 miles. Among many modifications made to the vehicle was a mount for a crane capable of carrying the tank's power train.

 On June 29th, 1944, the designation of the vehicle changed again, this time from "Medium Tank, T26E1" to "Heavy Tank, T26E1". The tank is described as "It has a weight of 43 tons, a maximum of 4" of armor giving 6.9" basis for frontal plates, and 24" tracks. Except for weight, thickness, and track width, it resembles the medium tank, T25E1".

2750 T26E1 heavy tanks were ordered, and 3188 T26E1 tanks armed with a 105 mm howitzer (later designated T26E2), despite the fighting compartment of the latter not having been designed yet. At this point, 122 T23 tanks have been made (including a prototype made in November of 1943), with the remaining 128 tanks due by October of 1944, 40 T25E1 tanks have already been manufactured, and 6053 T26 tanks are required for 1944 and 1945. 10 T26E1 tanks with 90 mm guns have been produced up to this point, with 105 more to come before the end of the year. The remainder of required T26E1 tanks armed with 90 mm guns and all T26E1 tanks armed with 105 mm howitzers will be produced in 1945.

Development of a tungsten carbide HVAP shell for the 90 mm gun began in July 1944, with the objective of penetrating a 6 inch plate at a 30 degree angle at 2000 yards.

The development of a T25E1 and T26E1 armed with a 75 and a 76 mm gun was ordered by the Commanding General, Army Ground Forces, on July 15th, 1944, but the Ordnance Department requested a low priority for this development, citing that "the 75-mm gun is now furnished in quantity in the Light Tank M24, the medium tanks of the M4 series, and the Assault Tank M4A3E2. The 76-mm gun is now being produced in quantity on the medium tanks of the M4 series."

The 10 finished T26E1s weren't sitting around gathering dust. As of November 10th, 1944, they went through approximately 20000 miles of testing, resulting in more changes to the design, such as a 23 inch track. Research continued into improving the cooling, braking, and ballistic performance of the vehicle.

In December of 1944, the tank was considered "far superior to any tank of equal speed or weight" by the Ordnance Committee. At this point, the improved tank was renamed T26E3, to avoid confusion with the ten pilot vehicles. Twenty tanks were shipped to Europe on February 7th, 1945, on the "Heavy Tank Mission", accompanied by Major General G.M. Barnes of the Ordnance Department. Ten tanks entered action on February 23rd, 1945, with the Third Armoured Division. A few days later, the other ten went into battle with the Ninth Armoured. 

The Heavy Tank, T26E3, nicknamed "General Pershing", was standardized as the Heavy Tank, M26 on March 29th, 1945.

Cross-section diagram of Heavy Tank M26 showing interior arrangement.

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