A committee was formed to help come up with a design, chaired by Sir Albert Stern, of which the members had been involved with tanks in World War I. The General Staff came up with specifications for a tank, the A20, that could re-fight World War I, in September 1939. These covered:
- infantry tank to go over ground cratered by fire and waterlogged
- able to go over moderate vertical obstacles and trenches
- 60 mm armor to defend against 37 mm antitank guns
- 10 mph speed
- 2 pdr main armament with a coaxial Besa MG in sponsons on each side, Besa MG and 2" bomb thrower by the driver
- main armament requirements were later updated to a 2 pdr and coaxial Besa MG in a Mark II pattern turret, a 2 pdr in the hull, and 2 Besa machine guns on each side of the hull
- weight of 37.5 tons
- the tank had to be transportable by British rail which limited its width and weight
The first prototypes of the A20 were completed in June 1940 by Woolwich and Harland & Wolff of Belfast. These were built from mild steel and were designated the A20E1, A20E2, A20E3, and A20E4. However, these resembled World War I type tanks. A pilot model was built, except for the turret, and was put through running trials. It didn't have the side sponsons, as requested in the specifications, but had a rather long hull. The small independently sprung road wheels were supposedly inspired by the French Char B1 bis.
The gearbox, designed by Dr. H.E. Merritt, had problems after only a short run. The Meadows 12 cylinder engine didn't produce the required power. Due to the weight of the vehicle coming close the the limit, as defined by the specifications, the 2 pdr gun in the hull would have to be excluded from the design.
In June 1940 the A20 was abandoned.
Creation of the A22
The specifications for the A22 were developed and Vauxhall Motors Ltd. of Luton, Bedfordshire, were to create the design and produce a vehicle straight from the drawing board. This expedited development schedule was because of France's capitulation and it was felt Germany would invade the United Kingdom at any moment. Vauxhall was asked to finish it within a year.
Dr. H.E. Merritt, Director of Tank Design, moved to Luton with a small staff worked on the A22 design. The A20 pilots had the new Bedford 12 cylinder engine installed and run.
It had been intended to have a larger gun than the 2 pdr installed in the turret, but it was the only one available at the time. Because it did not have high explosive (HE) ammunition it was decided to put a 3" howitzer in the front of the hull.
The first batch of 14 completed tanks were delivered on June 30, 1941. These initially had mild steel turrets that were signified by the "Caution Unarmored" plates on the turrets.
Most had to be modified before being issued to troops. Due to the rushed development there were numerous defects that led to many breakdowns. A War Office survey in November 1941 showed there were 16 modifications that were needed before the tank could sustain operations in the field. Most of these had to do with improvements needing to be made to the steering and transmission. Almost 1,000 vehicles had to be modified. Even with these changes, it was found in July 1942 that some tanks were failing after only 150 miles of use.
Vauxhall Motors eventually assigned some of their own engineers to the tank brigades so that they could learn what other modifications were needed.
In 1943 it was decided to stop production of the Churchill as it was decided that the A27 cruiser tanks would be more important due to their speed. However with the success in Tunisia it was decided to continue production.
The hull was made out of steel plates that were joined together by steel angles that were then riveted. To this the armor plates were bolted. Escape doors were installed on either side of the hull. These doors (except in the Mk VII and Mk VIII) have quick opening ports. There were double hinged doors above the driver and front gunner.
The suspension was compact and the "pannier" space was almost uninterrupted. This space was used for ammunition, equipment, and the fuel tanks.
The hull was split into four sections:
- the front, with the driver on the right, and on the left the gunner
- Below the driver's vision door was the steering control.
- A Lockheed hydraulic system was connected to the steering brakes.
- fighting compartment
- Turret was mounted on a ball race.
- The commander, gunner, and wireless operator were on a suspended platform.
- Turret was traversed by electric and hand.
- The radio equipment was on a shelf at the rear of the turret.
- engine compartment
- On the outside of the hull were heavy armored louvres protecting the air intakes. When transported by rail they could be removed.
- The Bedford horizontal drives the tracks through the rear sprockets.
- Their were 2 engines that shared a common crankshaft. The gas pump line was located under the engine and had a tendency to burst.
- gearbox and steering brakes
- A two cylinder Clayton Dewandre air compressor assisted the steering and clutching.
- Gearbox was transversely mounted and parallel to the final drive.
- The Churchill was the first British tank to use the Merrit-Brown regenerative steering system.
- 5 speed gearbox in early models was replaced by 4 speed which gave similar performance.
11 bogies each side, independently suspended. These wheels were 10" in diameter. Idler at front and driving sprocket at back.
Comparison of Main Tank Armament Performance