HMS Valiant was one of five Queen Elizabeth-class battleships built for the Royal Navy during the early 1910s. She participated in the Battle of Jutland during the First World War as part of the Grand Fleet. Other than that battle, and the inconclusive Action of 19 August, her service during the war generally consisted of routine patrols and training in the North Sea. She saw further action during the Second World War in the Mediterranean and Far East.

A limpet mine is a type of naval mine attached to a target by magnets. It is so named because of its superficial similarity to the shape of the limpet, a type of sea snail that clings tightly to rocks or other hard surfaces.

A swimmer or diver may attach the mine, which is usually designed with hollow compartments to give the mine just slight negative buoyancy, making it easier to handle underwater.