The Medium Tank T5 was the prototype for the Medium Tank M2, and was also the first in the series of designs that ended with the M4 Sherman.
In the period after the First World War the US Army had produced two series of medium tanks. The Medium Tank M1921/ M1922/ T1 family of the 1920s were designed within the Army, were underpowered, and never got beyond the prototype stage. The second, more promising, family, was based on the Christie M1928, the first vehicle to use the famous 'Christie suspension', with four large road wheels on each side and the ability to run with tracks or just on the road wheels. This family progressed through the Christie M1931/ Medium Tank T3 to the Medium Tank T4, which was eventually accepted in 1939 as the Medium Tank M1, limited standard, despite already being obsolete.
Work on a third family of tanks was approved by the Ordnance Committee on 21 May 1936. The new Medium Tank T5 was to abandon the convertible wheel or track suspension, and use as many components as possible from the successful Light Tank M2, including the suspension system.
The T5 benefited from earlier work on tank armament. The Medium Tank T4 had been produced in two different versions, one armed with a tank gun in a fully traversing turret, the other carrying five machine guns in a barbette - two in the front, and one each on the sides and rear. A third alternative had been suggested by Captain G. H. Rarey in April 1934. This carried four machine guns in the corners of the fighting compartment, with a turret on top.
Medium Tank T5, Phase I
The Medium Tank T5 used the same vertical volute spring suspension system as the Light Tank M2, but with three bogies instead of the two used on the M2. Each bogie carried two road wheels, each connected to a central mount by an almost horizontal pivoting arm. Each arm was supported by a vertical volute spring, which was braced against the top of the bogie unit. A volute spring is a spring in the shape of a cone, allowing the coils to slide over each other, and thus allowing for more vertical movement than on a normal spring of the same strength. They are normally made from a flat strip of metal which is then wound up to produce the spring (as seen on garden secateurs).
The T5 Phase I was given a roughly square fighting compartment, with the corners cut off and .30in machine guns mounted in barrel shaped sponsons with an open back inside the compartment, carried on the corners. The turret was mounted on top of this fighting compartment, and was to be armed with a new high velocity 37mm antitank guns. Two more machine guns were installed in the hull front, and two anti-aircraft guns could be carried.
The Phase I never received its high velocity gun. When first built it was given a wooden superstructure and turret with a mock gun. This was used in early tests between 16 November and 29 December 1937. The proper steel superstructure and turret was installed early in 1938, and the mock gun was retained. Later in the year two 37mm M2A1 guns were installed as a temporary measure, but they remain in place to this day.
The 250-268hp air-cooled Continental radial engine was at the rear of the tank, with the final drive at the front. The driver sat in a central position above the drive, and the front of the tank sloped down from his viewpoint to the sides and front. The hull front machine guns were at the base of the frontal armour.
The Phase I was sent to the Aberdeen Proving Grounds on 16 February 1938 where it performed well. The Chief of Infantry recommended that the T5 Phase I with 37mm high velocity gun should be standardized. The Ordnance Committee agreed on 2 June 1938, and shortly afterwards the design was standardized as the Medium Tank M2. The Phase I weighed just over 15 tons, so was somewhat lighter than the eventual M2,
T5 Phase II
The T5 Phase II was a design study that was never built.
T5 Phase III
The Phase III was produced to test out the same basic design but at a higher weight. The Phase III was given a more powerful 346hp Wright Radial engine, wider tracks and extra armour to bring the weight up to 20 tons. The driver's position was moved to the left, and a new asymmetrical nose designed. The Phase III kept the same machine gun armament as the Phase I, but did receive the high velocity 37mm gun T3 in mount T1, carried in a new cast turret. The Phase III underwent tests at Aberdeen in November-December 1938, where it was rated as very satisfactory, but about one ton over weight.
The T5E1 was the designation given to the T5 when it was used to test a 400hp Guiberson air-cooled radial diesel engine.
The T5E2 was a radical remodelling of the Phase III, carried out to test the value of mounting a 75mm gun in a tank. The right-hand side of the superstructure was modified to carry a 75mm pack Howitzer M1A1. The right-rear and both left-hand machine gun sponsons were retained, and a smaller six sided turret (or large cupola) with another .30in machine gun and an optical range finder was installed (this resembled a smaller version of a naval range finder, with tubes extending from both sides of the turret to carry the lenses of the range finder).
The T5E2 underwent tests at Aberdeen between 20 April 1939 and 8 February 1940. The 75mm howitzer proved to be very effective against tanks and area targets. The experience gained on the T5E2 would help with the design of the Medium Tank M3 (Lee/ Grant).
Stats T5 (Phase I)
Hull Length: 17ft 3in
Hull Width: 8ft 2in
Weight: 15 tons
Engine: Continental radial 7-cylinder air-cooled, 250hp
Max Speed: 31mph road speed
Max Range: 125 cruising range
Armament: One 37mm gun, six machine guns
Armour: 1in- 1/4in
Hull Length: 18ft
Hull Width: 8ft 7in
Height: 9ft 3in
Engine: Wright Radial 9-cylinder 346hp air-cooled
Armament: One 75mm howitzer, eight machine guns
Armour: 1 to 1 1/4in