The Colossus-class battleships were British ironclad warships, carrying their main armament in turrets, which served in the Victorian Royal Navy from 1882.

They were in all essential points improved versions of the Ajax class, with slightly greater displacement, protection and speed, with better handling characteristics, and most significantly, with breech-loading artillery replacing the obsolescent muzzle loaders.

In 1879, while the Colossus class was under construction, a 100-ton muzzle-loader was being tested at the Royal Arsenal, Woolwich, and the 16-inch 80-ton guns destined for HMS Inflexible were nearly complete.

Responding to a groundswell of professional opinion, the Admiralty sent a group of senior officers to witness and report on the performance of the new breech-loading weapons being produced by Krupp in Essen.

The Colossus class was nominated to be armed with these guns; the delay in their manufacture largely accounts for the protracted building times of these vessels.