page_title: Churchill tank
section_title: Design
hierarchical_section_title: Churchill tank / Design
caption_attribution_description: English: Close-up of drive wheels and tracks of Churchill Tank
context_page_description: The Tank, Infantry, Mk IV Churchill was a British heavy 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 design lay in the expectation that war in Europe might be fought in conditions similar to those of the First World War and emphasised the ability to cross difficult ground. The Churchill was rushed into production 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 had been built, a better-armoured version, the Mark VII, entered service. 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 more than 250 saw active service on the Eastern Front.
context_section_description: 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 1,296 cu in (21.238 L) capacity engine was rated at 350 bhp at 2,000 rpm, delivering 960 lb⋅ft (1,300 N⋅m) torque over an engine speed range from 800 to 1,600 rpm.
  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. There were final reduction gears, of the planetary type, in the driving wheels.
  The first turrets were of cast construction and were rounded in shape, providing sufficient space to accommodate the relatively small 2 pounder gun. To fulfil its role as an infantry support vehicle, the first models were equipped with a 3-inch howitzer in the hull in a layout very similar to the French Char B1. This enabled the tank to deliver a useful high-explosive capability while retaining the anti-tank capabilities of the 2 pounder. However, like other multi-gun tanks, it was limited by a poor fire arc - the entire tank had to be turned to change the aim of the hull gun. The Mk II dispensed with the howitzer and replaced it with a bow machine gun and on the Mk III, the 2 pounder was replaced with the 6 pounder, significantly increasing the tank's anti-tank capabilities. The tank underwent field modification in North Africa with several Churchills being fitted with the 75 mm gun of destroyed M4 Shermans. These "NA75" variants were used in Italy. The use of the 75 mm increased the effectiveness of the tank, as it was a generally superior weapon to the 6 pounder, possessing similar anti-tank capabilities, while also being considerably more effective when used in infantry support roles.
  Churchills made use of the Vicke
caption: Close-up of road wheels and tracks of Churchill Mk. VII
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