The Somerset cannon was a British cannon designed within the Admiralty and manufactured by Armstrong's. Its genesis was the unexpected failure of the Armstrong breech-loading rifles recently developed and installed on Royal Navy ships. The Somerset was a 6.5 ton 9.2-inch calibre smoothbore muzzle-loader, firing a 100-pound shot. With a charge of 33 pounds of gunpowder, a steel shot could penetrate 5.5 inches of armour at 800 yards.