That the observation from the inside of the machine was bad, and efficient fire control was, therefore, impossible.
That the means provided for entering and leaving the tank were unsatisfactory, and, in the case of the female machine, speedy evacuation in the event of fire was difficult.
That the whole of the petrol supply was carried inside the machine, and in a vulnerable position—a circumstance which added to the risk of fire in the event of a hit in the petrol tank by armour-piercing bullet or shell. Furthermore, gravity was the only means for transferring petrol from the main petrol tanks in the front of the machine to the carburetter, and, therefore, it frequently happened that when a tank “ditched” nose downwards, the petrol supply was cut off, and consequently the dangerous practice of “hand-feeding” had to be resorted to.
The Mark II and Mark III Tanks
These machines were produced in small numbers, and their difference from Mark I lay in various minor improvements, none of a radical nature.
The Mark IV Tank ([Plate I]—see [p. 26])
In 1917 this tank became the standard fighting machine of the Tank Corps, and it was used in battle throughout this year and the following. As already stated, in outline it corresponded so closely with the Mark I machine that a study here of the main features of this tank will serve generally as an illustration of what had taken place in tank development up to this date.
The machine was 26 ft. 5 in. long over all, whilst the width of the female over its sponsons was 10 ft. 6 in., and of the male, 13 ft. 6 in. The height of the machine was 8 ft. 2 in., and its weight, equipped, was 28 tons. The armament consisted, in the case of the male, of two 6-pounder guns and four machine-guns, and in that of the female of six machine-guns; it was fitted with a 105 h.p. Daimler 6-cylinder sleeve-valve engine which, at a later date, was replaced in a limited number by one of 125 h.p. This increased power was obtained by the use of aluminium pistons, twin carburetters, and by speeding up the engine.
Generally speaking, these engines gave very little trouble, although somewhat under-powered for the work they had to perform. They were, it may be added, particularly suitable from the maintenance point of view, owing to their “fool-proof” nature, due chiefly to the absence of the usual poppet-valve gear, with its attendant risk of maladjustment.
Power was transmitted from the engine flywheel, through a cone-type clutch and a flexible coupling, to a two-speed and reverse gear-box, known as the primary gear, this being under the direct control of the driver, who could thus obtain first and second speeds, or reverse, without other assistance.