The Ordnance QF Hotchkiss 6 pounder gun Mk I and Mk II or QF 6 pounder 8 cwt were a family of long-lived light 57 mm naval guns introduced in 1885 to defend against new, small and fast vessels such as torpedo boats and later submarines. There were many variants produced, often under license which ranged in length from 40 to 58 calibers, but 40 caliber was the most common version.
Early Elswick gun on recoil mounting
Mark I Male tank with a long QF 6-pounder 8 cwt gun, at the Bovington Tank Museum.
Hotchkiss 6-pounder being prepared to combat at the USS Detroit (L'Univers Illustré, 1894).
Mk II Shell base, showing fuze hole
The Vickers Medium Mark II was a British tank built by Vickers in the Inter-war period.
Vickers Medium Mk.IIA* at U.S. Army Ordnance Museum, Aberdeen
Australian Medium Mark II
Vickers Medium Mark II at the Bovington Tank Museum