British anti-invasion preparations of the Second World War entailed a large-scale division of military and civilian mobilisation in response to the threat of invasion by German armed forces in 1940 and 1941. The British Army needed to recover from the defeat of the British Expeditionary Force in France, and 1.5 million men were enrolled as part-time soldiers in the Home Guard. The rapid construction of field fortifications transformed much of the United Kingdom, especially southern England, into a prepared battlefield. Sea Lion was never taken beyond the preliminary assembly of forces. Today, little remains of Britain's anti-invasion preparations, although reinforced concrete structures such as pillboxes and anti-tank cubes can still be commonly found, particularly in the coastal counties.

HMS Revenge was the lead ship of five Revenge-class super-dreadnought battleships built for the Royal Navy during the First World War in the mid-1910s. The ships were developments of the Queen Elizabeth-class battleships, with reductions in size and speed to offset increases in armour protection whilst retaining the same main battery of eight 15-inch (381 mm) guns. She was laid down in 1913, launched in 1915 and commissioned in February 1916, early enough to be worked up to see action with the Grand Fleet at the Battle of Jutland in May that year. During the engagement, she engaged German battlecruisers, damaging two of them before being forced to turn away to avoid torpedoes that damaged her squadron flagship and caused the squadron to lose contact with the rest of the fleet. Revenge emerged from the battle unscathed, but she saw no further action during the war, as the British and German fleets turned to more cautious strategies owing to the risk of submarines and naval mines.