The Satsuma class (薩摩型戦艦, Satsuma-gata senkan) was a pair of semi-dreadnought battleships built for the Imperial Japanese Navy (IJN) in the first decade of the 20th century.

[3] The intended armament of these ships, laid down before HMS Dreadnought, would have made them the first "all big-gun" battleships in the world had they been completed to their original design.

[5] The construction of Aki was delayed since she could not be laid down until the slipway occupied by the armored cruiser Tsukuba was freed by that ship's launching.

The IJN took the opportunity provided by the delay to modify the ship to accommodate steam turbines and various other changes that generally increased her size.

[4] Aki was intended use the same type of engines as her sister, but the IJN decided fit her with a pair of Curtiss steam turbine sets after she was launched in 1907.

[10] The other major difference between the two ships was that Aki's secondary armament consisted of eight 45-caliber 6-inch (152 mm) 41st Year Type guns, mounted in casemates in the sides of the hull.

[11] Satsuma, in contrast, was equipped with a dozen quick-firing (QF) 40-caliber 4.7-inch (120 mm) 41st Year Type guns, mounted in casemates in the sides of the hull.

The IJN recognized that fact when it drew up the first iteration of its Eight-Eight Fleet building plan for eight first-class battleships and eight battlecruisers in 1910 and did not include them.

[16] Aki was refitting at Kure and Satsuma was assigned to the 1st Battleship Squadron when World War I began in August 1914.

[4] The latter served as Rear Admiral Tatsuo Matsumura's flagship in the Second South Seas Squadron as it seized the German possessions of the Caroline and the Palau Islands in October 1914.

[4] In the years immediately following the end of the war, the United States, Britain, and Japan all launched huge naval construction programs.