Only 100 Mark II and Mark III tanks were built, 100 fewer than the first model. Because of this, they are often referred to as a limited, transitional model, but the "twos" and "threes" had some unique features.
The Mark II got rid of the famous wheeled tail, allegedly necessary to help the tank cross trenches. Legend has it that the tail fell off one tank in battle, but the crew kept driving. It turned out that the rear wheels had no practical value. This shortened the tank by two meters with no damage to the performance. Instead of a tail, the rear of the tank now carried a toolbox. The exhaust pipes which were on the roof of the Mark Is were also moved to the rear.
The Mark III was an attempt to thicken the front armour with applique plates. Even though openings for their mounting were made, the extra armour was never installed. However, the Mark III was the first to carry an unditching beam, affixed to the roof. It was used as a means of freeing a bogged down tank. This measure was surprisingly useful and was used by all tanks in the future.
Mark IV: The first thousand
Mark IV in battle for Cambrai
In late 1917, work on new "rhombus" tanks stalled. In part, this was the fault of weapon manufacturers who feared that tanks will make their rifles, machineguns, and cannons obsolete, and so took every opportunity to impede tank production. However, even the will of "gun barons" could not stop the development of armoured vehicles, and in December of 1917, the Mark V, otherwise known as the "Ricardo tank" was ready for production.
Experience at the front showed that tanks need a more powerful engine that was capable of working through constantly changing load, and one that was simple enough for repairs on the front lines. Engineers could not expect to be allowed to use hardened steel or aluminium: aircraft manufacturers claimed those resources. The first person to develop a real tank engine was Henry Ricardo. His engine fully satisfied the requirements of the military. That and the new Wilson gearbox significantly simplified the driver's life.
More novelties on the Mark V include the light telegraph, which replaced signal flags. From May 1918 to the end of the war, the British army received 400 Mark Vs: 200 each of cannon "males" and machinegun "females".
On April 24th, 1918, the first tank duel came to pass: a Mark V against a German A7V. The battle proved that machinegun tanks are only good against infantry. As a result, some of the tanks had the machinegun in one sponson replaced with a cannon. These asymmetric tanks were jokingly called "hermaphrodites" by the soldiers.
Mark V at Passchendaele: Are tanks afraid of mud?
Mark IX: A rhombus for infantry