Tank Drawing

Etymology
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.