The Mark IV tank incorporated several automotive and structural improvements over earlier designs. One of the key characteristics of the British rhomboidal tanks was the primary armament being carried in external sponsons on both sides of the tank.
In previous marks, these sponsons were fixed and had to be removed to transport the vehicle by rail. Given that each sponson weighed over a ton, removal and reattachment were arduous tasks. The Mark IV's sponsons were, however, retractable, saving a great deal of time.
To ensure the vehicle wouldn't stall at steep angles of attack, the gravity fuel feed of the Mark I was replaced with a vacuum system. The final drive was also enclosed, based on experience with the Mark I.
Its six-cylinder Diamler engine provided 105hp, giving the 28-ton vehicle a top speed of about 4mph. The vehicle required a very large crew of eight to man the various armaments and control the vehicle. Simply steering the vehicle required the coordinated effort of four crewmen: the driver, two gearsmen, and the commander. The driver controlled the primary gearbox, the gearsmen controlled the high/low gear ratios separately on each track, and the commander controlled the brakes. Reverse gear was controlled by the driver, but the gear ratio was set fairly high, resulting in poor reverse performance for the vehicle, making it difficult for the Mark IV to un-ditch itself.
The Mark IV was produced in two major variants, 420 'male' tanks, which carried two six-pounder guns and three Lewis 303 machineguns; and 595 'female' tanks, in which the six-pounder guns were replaced with two additional Lewis machineguns.
Later in the war, as a result of combat experience in tank versus tank combat, some Mark IV female tanks had one of their machinegun sponsons replaced with a six-pounder sponson creating a Mark IV 'hermaphrodite'.
In addition to the combat tanks, over 200 tank tenders with boosted engines were built to carry tank supplies. These tenders had square, mild-steel sponsons, which easily distinguished them from the combat tanks.
Designed by Evan Allen
Painted by Victor Pesch
