With the introduction of the Mark V tank, which represents the standard British heavy tank of to-day, great progress was made in all-round speed, ease of manœuvre, radius of action, simplicity of control and feasibility of observation.
The dimensions and weight of this tank were approximately the same as those of the Mark IV, whilst the design of the hull still closely followed the lines of the original Mark I. Equipped with the 150 h.p. Ricardo 6-cylinder poppet-valved engine, specially designed for tank work, the advent of the Mark V machine called for the introduction of new courses of instruction for the personnel of the Corps, very few of either officers or other ranks having, at this time, any experience of the care and adjustment of the valve gear.
This Ricardo engine, of somewhat unorthodox design, was highly efficient and, with proper care and attention, gave very little trouble. From the engine, power was transmitted through a plate clutch in the flywheel to a four-speed gear-box, immediately in rear of which was the reverse gear, providing “reverse” on all speeds. The cross-shaft, incorporated with the reverse gear, carried at either end (in the same relative position as the secondary gears, explained in dealing with the Mark IV machine) an epicyclic gear. It is not within the scope of this chapter to describe this gear in detail, but it may be regarded as serving the double purpose of a reduction gear and clutch, combined in one unit.
From these epicyclic gears, the transmission of the drive through to the tracks followed the principle of the Mark IV machine, except that there was no second-line pinion assembly as in the secondary gear of the earlier tank, the Coventry chain on the Mark V passing direct from the single-unit epicyclic gear to the pinion assembly operating the track driving wheels.
All the items enumerated above were under the direct control of the driver, who was therefore enabled to perform, single-handed, all the operations which previously required the work of four men. Hand levers controlled the epicyclic gears, primary gear-box, and reverse gear, whilst the clutch and gear were foot-operated.
To steer the tank at any speed, the driver had merely to raise the epicyclic gear lever on the side on which he wished to turn. This had the effect of interrupting the drive to that track, so that, being driven by the remaining track, the machine would turn upon the “idle” side.
Where a sharp “swing” was necessary, application of the foot brake would automatically check the “idle” track, this being allowed for by means of a single compensating link motion with which the controls were interconnected.
The engine was petrol-fed by the autovac system, as fitted to the later Mark IV machines. Cooling of the engine was effected by means of a tubular type radiator, the water therein being itself cooled by air drawn from outside the tank, through louvres in the left-hand wall of the hull, and finally expelled through similar louvres in the right-hand wall.
Further, the engine was completely enclosed in a sheet-iron casing, from which the hot foul air was exhausted through the roof of the tank by means of a Keith fan.
The Mark V armament corresponded with that of the Mark IV, whilst the sponsons were of similar design to those fitted to the latter type.