Cromwell Tank - Design

Design

The frame was of rivetted construction though welding was used later. The armour plate was then bolted to the frame; large bosses on the outside of the plate were used on the turret. Several British firms besides Leyland contributed to production of the Cromwell and Centaur including LMS Railway, Morris Motors, Metro-Cammell, Birmingham Railway Carriage and Wagon Company and English Electric. Some variants were produced with 14-inch-wide (360 mm) tracks, later 15.5-inch tracks were used.

The suspension was of the Christie type with long helical springs (in tension) angled back to keep the hull sides low. Of the five roadwheels each side, four had shock absorbers. The tracks were driven by sprocketed wheels at the rear and tension adjusted at the front idler; this being standard British practice. The side of the hull was made up of two spaced plates, the suspension units between them, and the outer plate having cutouts for the movement of the roadwheel axles. The gearbox had five forward and one reverse gears. The first gear was for "confined spaces, on steep inclines or...sharp turns".

The Meteor engine delivered 540 hp at 2,250 rpm. This was the maximum rpm which was limited by governors built into the magnetos. Fuel consumption on "pool" petrol (67 octane) was between 0.5 and 1.5 miles per gallon depending on terrain.

The driver was sat on the right in the front of the hull, separated from the hull gunner by a bulkhead. The driver had two periscopes and a visor in the hull front. The visor could be opened fully or a small "gate" in it opened; in the latter case a thick glass block protected the driver. A bulkhead with access holes separated the driver and hull gunner from the fighting compartment. A further bulkhead separated the fighting compartment from the engine and transmission bay. The engine compartment drew cooling air in through the top of each side and the roof and exhausted it to the rear. To allow fording through up to 4 ft (1.2 m) deep water a flap could be moved over to cover the lowermost air outlet. Air for the engine could be drawn from the fighting compartment or the exterior; it was then passed through oil bath cleaners.

The Cromwell still had revisions to make before service, most notably changing from the QF 6-pounder (57 mm) to the ROQF 75 mm gun, which was an adaptation of the 6 pounder design to fire the ammunition of the US M3 75 mm gun, which gave it a better HE round to use in infantry support. This meant the 75 would use the same mounting as the 6 pounder however it was not until June 1944 that Cromwell first saw action during Operation Overlord, the Allied invasion of Normandy. It had a mixed reception by crews. It was faster and had a lower profile than the Sherman tank and thicker frontal armour; 3 in (76 mm) versus the 2 in (51 mm) of the Sherman. On later Cromwells this was increased incrementally, first to 3+1⁄₄ in (83 mm), then finally to 4 in (100 mm). The 75 mm gun, though able to fire a useful HE shell, was not as effective against armour as the 6 pdr or the Ordnance QF 17 pounder gun though it was more powerful than the original 75 mm gun mounted on the Sherman. A derivative of Cromwell was begun to take the 17 pounder, this fell behind and in practice the majority of the 17 pounder gun armed tanks to see service in the war were Firefly variant of the Sherman.

There was a 7.92 mm Besa machine gun mounted coaxially to the main armament operated by the gunner. A second was "gimbal" mounted in the front of the hull. The mounting gave 45 degress of coverage to the front (it had 25 degrees of vertical movement as well) and sighting was by a No. 35 telescope which was connected through a linkage to the mounting.

In the top of the turret was mounted a 2 inch "bombthrower" angled to fire forward. Thirty smoke grenades were carried for it.