The Nagato-class battleship Mutsu of the Imperial Japanese Navy was laid down in 1918, launched in 1920, and commissioned in 1921. She was one of the "Big 7" battleships allowed to retain 16-inch guns under the Washington Naval Treaty. She played a significant role in Japan's interwar policy. During the Second World War, Mutsu participated in several operations, including the Battle of Midway and the Guadalcanal campaign, though she never engaged in direct combat. Her career came to an end on 8 June 1943 when a magazine explosion at Hashirajima anchorage split the ship in two, resulting in the loss of 1,121 crew members.

The IJN Mutsu was introduced in Update "Alpha Strike". She was the first 16-inch vessel in the game, trading excellent damage output for lower survivability, particularly due to her aft magazines being exposed above the waterline. She is also a very easy target for enemy bombers, being defended solely by four 76 mm guns. Overall, though, she is an excellent surface combatant and one of the most dangerous enemies in the top tier.