Rocastle: We need water for the Vickers gun.
The Vickers .303 Machine Gun became the standard in the British Army from 1912 to 1960. Being water-cooled, it could fire continuously for long periods. Heat engendered by the rapid fire soon boiled the water and caused a powerful emission of steam, which was condensed by passing it through a tube into a canvas bag of water. By this means the gun could continue to fire without a cloud of steam giving its position away to the enemy.