The Tank, Infantry, Mk IV (A22) Churchill was a British infantry tank used in the Second World War, best known for its heavy armour, large longitudinal chassis with all-around tracks with multiple bogies, its ability to climb steep slopes, and its use as the basis of many specialist vehicles. It was one of the heaviest Allied tanks of the war.
The origins of the Churchill's design lay in the expectation that war in Europe might be fought in conditions similar to those of the First World War, and thus emphasised the ability to cross difficult ground. The Churchill was hurried into production in order to build up British defences against a possible German invasion. The first vehicles had flaws that had to be overcome before the Churchill was accepted for wide use. After several marks (versions) had been built, a better-armoured specification, the Mark VII, entered service with the British Army. The improved versions performed well in the later stages of the war.
The Churchill was used by British and other Commonwealth forces during the North African, Italian and North-West Europe campaigns. In addition, 344 Churchills were sent as military aid to the Soviet Union during the Second World War and 301 to 344 Churchill tanks saw active service on the Eastern Front.
Name The Churchill tank was named after John Churchill, 1st Duke of Marlborough. Winston Churchill told Field Marshal Jan Smuts "That is the tank they named after me when they found out it was no damn good!"p. 101, Victor Sims, Churchill the Great, The Best Stories, The Daily Mirror Newspapers Ltd, 1962
The name only incidentally matched what became the British Army practice of giving service names beginning with C to tanks. Cruiser tanks were given names, such as the contemporary Covenanter, Crusader, Cromwell, Cavalier and Comet but infantry tank naming had no particular pattern.
History A20
Initially specified just before the outbreak of the Second World War, the A20 (its General Staff specification) was to supplement the Matilda II and Valentine infantry tanks. In accordance with British infantry tank doctrine and based on the expected needs of attacking a fixed defensive line, crossing wide trenches, possibly shell-cratered ground similar to First World War trench warfare it was to be immune to the current German 3.7 cm Pak 36 anti-tank guns and carry an unditching beam.
A general outline produced by Woolwich Arsenal was expanded by Belfast shipbuilders Harland & Wolff with advice from the Department of Tank Design. The General Staff had proposed that it was armed with two QF 2 pounder guns, each located in a side sponson with a coaxial Besa machine gun. A third Besa and a smoke projector would be fitted in the front hull. To reduce weight the specification was revised to prefer a maximum armour to the front of 60 mm – sufficient to protect against ordinary shells from the German 37 mm gun. Outline drawings were produced by Woolwich Arsenal based on the A12 Matilda turret – the Director of Mechanisation opposed a turretless design – and the engine and Wilson epicyclic transmission being developed for the A13 Mark III Covenanter tank. Detail design and construction of the A20 was left to Harland & Wolff, who completed four prototypes by June 1940. During the construction period, the armament was reconsidered, including fitting either a 6-pounder gun or the French short 75 mm gun (as used on Char B1) in the forward hull – the former was considered too longIt was thought the muzzle might catch in the ground, and a shortened version would have poor ballistics and the latter would require redesigning the front of the hull. In the end, a 3-inch howitzer was chosen.Fletcher p. 21Perrett, p. 4 The A20 designs were short-lived, however, as at roughly the same time the defeated British Expeditionary Force was evacuated from Dunkirk. While intended for "positional warfare" and direct assaults against fortifications (it was referred to as "Shelled Area Tank", or by the French phrase Char de Fortresse) which had been rendered pointless by the fast pace of German armoured warfare, a heavy tank that could defend the infantry from other tanks was still desired.
At an initial 32 tons, with a 300 hp flat-12 Meadows DAV engine, the A20 had limited power compared to the 16-ton Covenanter. This was a less serious limitation than it might appear, owing to the British distinction between the high-speed cruiser tanks and the slow-speed infantry tanks. Vauxhall, who were already involved as consultants on the suspension, were approached to see if they could build the A20 and one example was sent to Vauxhall at Luton to see if they could provide an alternative engine developing 350 bhp. To this end, they developed a flat-12 petrol engine.Fletcher, pp. 21, 58 For speed of production, this engine was based on a Bedford Vehicles (Vauxhall's commercial vehicle operations) six-cylinder lorry engine, giving rise to its name of "Twin-Six". Although using sidevalves to fit within the space, the engine was developed with high squish pistons, dual ignition and sodium-cooled exhaust valves in Stellite seats to give 350 bhp.
A22 With France lost, the scenario of trench warfare in Northern Europe was no longer applicable and the design was revised by Dr H. E. Merritt,Who was also responsible for the triple differential design of the Merritt-Brown gearbox used in the Churchill. Director of Tank Design at Woolwich Arsenal, based on the combat witnessed in Poland and France. These new specifications, for the A22 or Infantry Tank Mark IV, were given to Vauxhall in June 1940."Fabrication of the new Churchill Tank, MK VII"
With a German invasion of Britain looking imminent, and the loss of a substantial amount of military vehicles in the evacuation from France, the War Office specified that the A22 had to enter production within a year. By July 1940, the design was completed and by December of that year the first prototypes were completed; in June 1941, almost exactly a year as specified, the first Churchill tanks began rolling off the production line.
A leaflet from the manufacturer was added to the User Handbook, which also described known faults, with work-arounds and what was being done to correct the problem. It said:
Harold Drew of Vauxhall achieved miracles with the Churchill and its Merrit-Brown Tank Gearbox produced by David Brown Limited; "a brilliant design that went into production off the drawing board without adequate prototype testing and had the most disastrous teething troubles" according to Robotham, but British tanks were under-powered, under-gunned and unreliable. At the Tank Board level the Director of Artillery was still extolling the merits of the 2-pounder, and this gun was still fitted to every British tank until March 1942.introduction of the 6-pounder gun into British use was delayed by the need to re-arm after the loss of equipment and production did not start until October 1941 and some designs in production could not take the larger gun In a 1942 exercise, one tank had to have its gearbox changed five times.
Because of its hasty development, there had been little testing and the Churchill was plagued with mechanical faults. Most apparent was that the Churchill's engine was underpowered, unreliable, and difficult to access for servicing. Another serious shortcoming was the tank's inadequate armament, the 2 pounder (40 mm) gun, which was improved by the addition of a 3-inch howitzer in the hull to deliver a HE shell, albeit not on a howitzer's usual high trajectory.
Production of a turret to carry the QF 6 pounder gun began in 1941, but lack of supplies of the plate used in an all-welded design led to an alternative cast turret also being produced. These formed the distinction between Mark III and Mark IV.Fletcher p. 59
In August 1942, the Churchill was used offensively for the first time in the Dieppe Raid.
The poor speed of the Churchill nearly caused production to be ceased in favour of the forthcoming Cromwell tank; it was saved by the successful use of the Mk III at the Second Battle of El Alamein in October 1942.
The second major improved Churchill, the Mk VII, was first used in the Battle of Normandy in 1944. The Mk VII improved on the already heavy armour of the Churchill with a wider chassis and the British 75 mm gun, which had been introduced on the Mk VI. It was primarily this variant, the A22F, which served through the remainder of the war. It was re-designated A42 in 1945.
The Churchill was a versatile project and was used in numerous specialist roles.
Design
The hull was made up of simple flat plates, which were bolted together in earlier models and were welded in later models. The hull was split into four compartments: the driver's position at the front, then the fighting compartment including the turret, the engine compartment, and the gearbox compartment. The suspension was fitted under the two large "panniers" on either side of the hull, the track running over the top. There were eleven bogies either side, each carrying two 10-inch wheels. Only nine of the bogies normally took the vehicle weight, the front coming into play when the vehicle nosed into the ground or against an obstacle, the rear acting in part as a track tensioner. Due to the number of wheels, the tank could survive losing several without much in the way of adverse effects as well as traversing steeper terrain obstacles. As the tracks ran around the panniers, escape hatches in the side could be incorporated into the design. These were retained throughout the revisions of the Churchill and were of particular use when the Churchill was adopted as the AVRE.
The Bedford Vehicles engine was effectively two engines in horizontally opposed configuration ("flat twelve") on a common crankshaft. There were four Solex carburettors each on a separate manifold that fed three cylinders formed as a single cylinder head. The elements of the engine and ancillary components were laid out so they could be reached for maintenance through the engine deck covers. Air for the engine was drawn from the fighting compartment through air cleaners. Cooling air was drawn into the engine compartment through louvres on the sides, across the radiators and through the engine compartment by a fan driven by the clutch. This fan blew the air over the gearbox and out the rear of the hull. By opening a flap between the fighting compartment and the engine compartment, this airflow could be used to remove fumes produced by firing the armament. The capacity engine was rated at at 2,200 rpm, delivering torque over an engine speed range from 800 to 1,600 rpm. With the introduction of the Churchill Mk VII and VIII, the engine was uprated to at 2,200 rpm, presumably to counteract the increased weight.
The gearbox featured a regenerative steering system that was controlled by a tiller bar instead of the more commonplace brake levers or, as with the German Tiger I heavy tank, a steering wheel. The tiller was connected, with servo assistance, hydraulically to the steering brakes. The Churchill was also the first tank to utilise the Merritt-Brown triple differential gearbox, which allowed the tank to be steered by changing the relative speeds of the two tracks; this effect became more pronounced with each lower gear, ultimately allowing the tank to perform a "neutral turn" when no gear was engaged, where it could fully pivot within its own length and thus rotate in place. There were final reduction gears, of the planetary type, in the driving wheels.David Fletcher, Churchill Infantry Tank, Osprey Publishing, , 2019, p. 11 Although capable of the noise at that speed was so great that the Churchill was limited to by not using the highest gear.