HMS London, pennant number C69, was a member of the second group of the County-class heavy cruisers of the Royal Navy. She and her sisters; Sussex, Shropshire, and Devonshire differed from the earlier group of Counties,, by having a smaller forward superstructure, which was positioned slightly further aft, and little armour plating. HMS London's career spanned over twenty years.

The County class was a class of heavy cruisers built for the Royal Navy in the years between the First and Second World Wars. They were the first post-war cruisers constructed for the Royal Navy and were designed within the limits of the Washington Naval Treaty of 1922. Such ships, with a limit of 10,000 tons standard displacement and 8-inch calibre main guns may be referred to as "treaty cruisers".