Churchill tank

The iconic Churchill tank is a heavy infantry tank used by the British in the Second World War. Originally intended to be used in trench warfare, the heavily armoured and slow Churchill tank quickly found itself in a new kind of war - dynamic warfare. Nevertheless, the tank went through numerous production variants and modifications and saw service in North Africa and North-West Europe. The versatility of the Churchill also led to successful specialist vehicles such as the Churchill AVRE and the Crocodile.

Background
The ultimate incarnation of the infantry tank concept, the first version of the tank was designed with the expectation that fighting in Europe would be similar to the trench warfare of World War I. The A20, as it was designated, was quickly retired after the Dunkirk Evacuation, with the new specifications for an A22 infantry tank given to Vauxhall in June 1940. Fearing a Nazi invasion, the War Office specified that the design enter production within a year. And it did: The first Churchills rolled off the production line in July 1941.

The rapid pace of development resulted in many flaws and shortcomings, primarily caused by an underpowered engine and a weak 2-pounder gun mounted in the turret, somewhat compensated by a 3-inch howitzer mounted in the hull. Further iterations on the design eliminated many of them, with the Churchill Mk III finally proving itself in combat at the second Battle of El Alamein in October 1942. Subsequent versions became the basis for several specialized variants and an indispensable part of Allied combat units, as they combined protection with maneuverability: The Churchill wasn't fast, but its suspension and all-around tracks allowed it to climb slopes other tanks could not.

Mark IV
The Mark IV was an iterative development of the Mark III, which was a major overhaul of the Churchill series, replacing the hull howitzer and 2-pounder with a more powerful 6-pounder (57mm gun). By numbers it was the most numerous variant produced, at 1,622 tanks. 
 * Churchill IV (SD2): The standard variant.
 * Churchill IV (Sov): A lend-lease variant of the above.
 * Churchill IV CMD: A company commander's tank.
 * Churchill OP (140mm) (SD2): An artillery observation tank.

Mark IV/Mark VII Crocodile
The Churchill Crocodile was a British flame-throwing tank of late Second World War. It was a variant of the Tank, Infantry, Mk VI (A22) Churchill VII, although the Churchill Mark IV was initially chosen to be the base vehicle. It was introduced as one of the specialized armored vehicles developed under Major-General Percy Hobart, informally known as "Hobart's Funnies". It was produced from October 1943, in time for the Normandy invasion. Used by units of the 79th Armoured Division in concert with the Churchill AVRE, and other Funnies, the flamethrower tank was an effective assault weapon whose threat could induce enemy troops to retreat or surrender. However, it was a specialized weapon limited by the short range of its flamethrower. On the other hand, it was used so successfully against bunkers that many surrendered after the first ranging shots.
 * Crocodile (SD2)

Mark IV/Mark VII AVRE
The AVRE (Assault Vehicle Royal Engineers) was a variant developed by the Canadian Army as a result of the Dieppe Raid. The inability of armor or infantry to effectively penetrate the beach defenses during the landings dictated the need for a new design and the AVRE was the answer. It was a Churchill Mark III or Mark IV with the gun swapped out for a recoiling spigot mortar, affectionately called the Petard. It fired a 290 mm (11 in), 40 lb (18 kg) projectile containing a 28-pound high-explosive warhead, capable of demolishing any reinforced position in short order.

By the time of the invasion of France in June 1944, 180 AVREs have been converted. They were first deployed in Normandy by the 79th Armoured Division on D-Day, rapidly proving themselves to be crucial assets in neutralizing Nazi fortifications. The design was so successful that it continued to serve beyond the end of the war, built on the Churchill VII chassis.
 * AVRE (SD2)

Mark V
The Churchill Mk. V was a Churchill IV refitted with QF 95mm howitzer, to provide infantry with fire support.
 * Churchill V (SD2)

Mark VI
The VI was a stopgap model produced with the QF 75mm tank gun, intended to serve until the introduction of the superior Churchill Mk. VII, the second redesign of the tank. Only 200 were produced. 
 * Churchill VI (SD2): The standard model.
 * Churchill VI CMD: A company commander's tank.

Mark VII
The Churchill VII was a redesigned, upgraded version of the Churchill. Mounting the standard QF 75mm tank gun, the Churchill VII had much thicker armor than the preceding model, comparable to that of a Tiger, allowing it to survive where other Allied tanks would falter. The ability to convert the tank into the Crocodile without special facilities was one of its major features. 1,600 were produced. 
 * Churchill VII: The standard model.
 * CMD Churchill VII: A company commander's tank.