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the insistent demand from the front the national energies had been turned to the making of guns and ammunition of all types, and prodigious quantities had been produced. But after the battle of Loos it began to be realized that even a great concen- tration of artillery and the expenditure of an immense amount of ammunition in a prolonged bombardment from guns of all calibres was not necessarily effective against such defences as the Germans had created, and could not insure that the assault- ing infantry would not be held up by uncut wire and suffer ter- rible loss from concealed and protected machine-guns. Some other means of dealing with the numbers of these weapons which would survive a bombardment even of the heaviest nature was necessary. As a result of the performance of the experimental tank in Feb. 1915, G.H.Q. France came to the

FIG. I. Mark I. Tank.

conclusion that such machines might be of some assistance, and made a demand for 4O. 1 This number was increased by the British War Office to 100, and supply was undertaken by the Tank Supply Committee of the Ministry of Munitions, com- posed of members representing interests directly concerned, under the chairmanship of Maj. (later Sir) Albert Stern. Orders were placed on Feb. 12, and production was commenced at once with the utmost secrecy, under great difficulties of labour and material owing to the great national effort then in full swing to produce munitions of all sorts.

During this initial period of manufacture various minor im- provements of the original design were incorporated. The

1 The first order placed by the French army headquarters, without awaiting the construction of an experimental machine was for 400 machines, and this was increased to 800.

sample machine, in accordance with the original specification for a machine-gun destroyer, was armed with two 6-pdr. guns and three Hotchkiss machine-guns. It was soon realized that, though effective for its purpose, this armament was deficient in man-killing fire-power for self-defence in the event of attack by large numbers of men, and it was decided to arm a certain pro- portion of tanks with four Vickers machine-guns instead of two 6-pounders. They were known as " females," the gunned machines being known as " males." The total number under construction was 150, half males and half females.

The Mark I. Tank (see figs. land 2). Details of this machine are given in the table on p. 697, but since all the succeeding machines were a development of it, some further description is given. Its main characteristic was the all-round track, which gave it its climb- ing power. This was perpetuated in all the British heavy tanks, though in the medium, or " Whippet," tanks evolved later, the same result was obtained by the projection of the tracks which were not under the machine. The essential value of both forms of construc- tion was that whatever the fore and aft angle of the machine with the horizontal a gripping surface was presented. This was achieved by the high, curved bows, rendered possible by combining the body and the chassis of the machine and using the sides of the body to support the tracks. The length was 32 ft. 6 in., over all, and 21 ft. 5 in. without the tail. The width was 13 ft. 9 in.; the height 8 ft. \ inch. Power was given by a six-cylinder sleeve valve Daimler engine of 105 H.P. ; transmission consisted of a cone clutch, primary (two speed) gear box (controlled by the driver) differential secondary (two speed) gears, actuated by hand levers, one to each track, and chain drives to the driving sprockets at the rear of each track. There Were thus four speeds ahead. This system necessitated a " gearsman " at each side, and was inconvenient and clumsy. The petrol feed was by gravity. There was no silencer. The armour plate varied from 12 mm. thickness in front to 6 mm. at the top and on the belly, the only part proof against the German " K " (armour-piercing) bullet being that 12 mm. thick. The armament of the male tank comprised two 6-pdr. guns, one on each side and four Hotchkiss machine-guns, and that of the female tank two Vickers machine-guns on each side and three Hotchkiss machine-guns. Owing to the pressure of time certain details in the design and equipment of the machine were adopted in order to employ material which was in production and quickly obtainable without waiting for special manufacture. The power unit, including the engine, with gear-box and differential was adopted because it was the standard power unit of an existing tractor and already in production. The 6-pdr. gun was adopted not because it was considered the best for dealing with machine-guns (the 2-pdr. automatic gun was originally specified), but because the Admiralty had a large number of these guns in hand and promised to supply the requisite number to the army. The 6-pdr. proved, how- ever, to be a very good weapon for its purpose. The male tank car- ried 324 rounds of 6-pdr. common shell for the 6-pdr. gun and 6,272 rounds of S. A. A.; the female carried 31,232 rounds of S.A.A. 8 The crew consisted of one officer and seven other ranks. The driver sat with the officer in the conning tower in front. The total weight of the male tank when loaded was 28 tons; of the female 27 tons. The average speed across country was 2 m. per hour, and the radius of action, nominally 23 m., averaged 12 m. over rough ground. The


 * It was originally proposed to carry a certain proportion of case shot. This was not done, but it was found necessary later to do this.

FIG. 2. Mark I. Tank.