HMS Lion was to be the lead ship of a class of six battleships built for the Royal Navy in 1939. The class was born out of the "Escalation Clause" of the Second London Naval Treaty of 1936, which nullified any prior tonnage restrictions imposed by the treaty, as well as those established by the preceding Washington and First London Naval Treaties, triggered in 1937 after Japan refused to ratify the treaty. As the then-latest battleship of the RN, the King George V class, was already late in construction, a decision was made to build a new battleship class based on the KGV's design in 1938. This was partly to save time during its construction.

Out of six ships, only two, Lion and Temeraire, were laid down. Lion was laid down at Vickers' High Walker Naval Yard in Newcastle-upon-Tyne on 4 July 1939, a month after Temeraire. However, the outbreak of World War II two months later effectively halted the construction of both ships. Due to the extreme wartime secrecy, no photographs of either ship are known to exist, leaving only written accounts of the ship's subsequent design modifications for historians. As the obsolescence of battleships became increasingly apparent as the war went on, the RN cancelled the construction of the Lion-class in 1944 to prioritise finishing the construction of HMS Vanguard.

HMS Lion was introduced in Update 2.59 "Sky Odyssey", and is presented in-game in her late 1938 design, more specifically the "Design 16F-38 Modified" configuration. As the successor to Prince of Wales, Lion features similar strengths and weaknesses: her nine 16-inch BL 16-inch Mark II guns offer decent penetration but low post-penetration damage, while her mobility is a noticeable improvement over her predecessor. While not as impressive as her contemporaries, Lion's secondary and AA armament is sufficient to ward off enemy aircraft. However, the ship remains vulnerable to plunging shells, as well as weak bulkhead armour.