The weight of the machine was carried upon the track by means of rollers, whilst the track was supported on the top of the hull by skids or rails.
Adjustment of track was effected by the movement of an “idler” wheel, which guided the track over the nose of the hull.
Refinements to the transmission were introduced in the shape of guards to protect the driving chains from mud, and also means were provided to lubricate the secondary gear-wheels with oil. It is recalled that, prior to the introduction of the chain-guard, the inside deck of the tanks was often covered with a layer of liquid mud, several inches deep, carried in by the chains, and delivered through the secondary gears.
Petrol was supplied to the engine in the earlier days of the Mark IV machine by a pressure-fed system which gave a great deal of trouble, and, being also considered dangerous, was finally discarded in favour of the Autovac system, which sucked the fuel from the main supply in a tank outside of the machine and delivered it to the carburetter by gravity.
Cooling of the engine was primarily effected by a copper envelope radiator, which gave some trouble and was finally superseded by a tubular type.
An efficient silencer, with a long exhaust pipe carried right to the rear of the machine, considerably reduced engine noise and rendered the approach march a far less hazardous undertaking than was the case with the earlier models.
Sponsons were designed to collapse into the interior of the machine when necessary, and the cumbersome practice of detaching them from the hull came to an end. Short 6-pounder guns were introduced to render this change possible.
Detachable “spuds,” to provide a grip for the tracks on difficult soil, were first introduced for this machine, as also was a highly efficient unditching gear. The latter consisted of a beam, rather longer than the overall width of the tank hull, which was fastened by clips and chains to each track, and, in passing round under the machine, actually took a purchase from the obstruction under the belly of the tank.
Detail improvements to give easier entrance and more rapid egress in case of emergency, as well as better and safer vision and fire control, were also introduced.