Tosa (土佐) was a planned battleship of the Imperial Japanese Navy. Designed by Yuzuru Hiraga, she was envisioned as the lead ship of the Tosa class of two 39,900-long-ton (40,540 t) ships. The battleships would have been armed with ten 410 mm (16.1 in) guns and bring Japan closer to its goal of an "Eight-four" fleet (eight battleships and four battlecruisers). However, after the Washington Naval Conference and the signing of the Washington Naval Treaty, all work on the ship was halted. With the vessel required to be destroyed in accordance with the terms of the treaty, the incomplete Tosa was then subjected to various tests to gauge the effect of Japanese weaponry before being scuttled on 9 February 1925.