Tank Drawing

The word tank was first applied to the British "landships" in 1915, before they entered service, to keep their nature secret. Several explanations of the precise origin of the term have been suggested, including:
It arose in British factories making the hulls of the first battle tanks: workmen and possible spies were to be given the impression they were constructing mobile water tanks for the British Army, thus keeping the production of a fighting vehicle secret.
The term was first used in a secret report on the new motorised weapon presented to Winston Churchill, then First Lord of the Admiralty, by British Army Lt.-Col. Ernest Swinton.
Winston Churchill's biography states, "To disguise the device, drawings were marked "water carriers for Russia." When it was pointed out this might be shortened to "WCs for Russia," the drawings were relabeled "water tanks for Russia." Eventually the weapon was just called a tank. (In fact, the prototype was referred to as a water-carrier for Mesopotamia. The Russian connection is that some of the first production Tanks were labelled in Russian "With Care to Petrograd," as a further security measure.)