Shell casing Britse QF 6 ponder 1917

The original QF 6 pounder naval gun had turned out to be too long for practical use with the current British heavy tank designs, which mounted guns in sponsons on the side rather than turrets on top as modern tanks do. The muzzles of the long barrels sometimes dug into the mud or struck obstacles when the vehicle crossed trenches or shell craters. The shortened QF 6 pounder 6 cwt Mk I of single tube construction was introduced in January 1917 in the Mark IV tank, and may be considered the world's first specialised tank gun.