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 in (23 cm) calibre smoothbore muzzle-loader, firing a 100 lb (45 kg) shot.
With a charge of 33 lb (15 kg) of gunpowder, a steel shot could penetrate 5.5 in (14 cm) of armour at 800 yd (0.73 km).
Providing a mounting which could reliably be worked at sea proved difficult for a piece of this size.
The gun was issued for service, and was mounted in HM Ships Achilles, Research, Favorite and Enterprise, but its performance was so poor, largely due to difficulties in controlling the gun, that it was withdrawn from service.