HMS Achilles was an armoured frigate built for the Royal Navy in the 1860s. Upon her completion in 1864 she was assigned to the Channel Fleet. The ship was paid off in 1868 to refit and be re-armed. When she recommissioned in 1869, she was assigned as the guard ship of the Fleet Reserve in the Portland District until 1874. Achilles was refitted and re-armed again in 1874 and became the guard ship of the Liverpool District in 1875. Two years later, she was rejoined the Channel Fleet before going to the Mediterranean in 1878. The ship returned to the Channel Fleet in 1880 and served until she was paid off in 1885.

The RML 7-inch guns were various designs of medium-sized rifled muzzle-loading guns used to arm small to medium-sized British warships in the late 19th century, and some were used ashore for coast defence.