Displacing 39,900 long tons (40,540 t) and armed with ten 410 mm (16.1 in) guns, these warships would have brought Japan closer to its goal of an "Eight-four" fleet (eight battleships and four battlecruisers).

Tosa and its sister ship Kaga were intended to be the second set of high-speed battleships (after the Nagato class) under the plan, and were approved for construction in the Diet's 14 July 1917 warship-building authorization.

[13] The barbettes for the 410 mm (16.1 inch) guns were in place, but no turrets or weapons had been mounted, so the holes in the main deck were covered with a mesh-like material.

Both breached the side protection system—allowing 1,008 and 726 long tons (1,024 and 738 t) of water, respectively, to enter the ship—showing that the usual three-compartment, all-void system used in most Japanese battleships was an insufficient defense against modern torpedoes.

This caused "extreme structural damage above the waterline" to Tosa, and confirmed that any problem in that part of the ship could seriously harm it.

Possible solutions included the installation of additional armor over the room or the use of walls on one side of the magazine that would be blown out and away from the ship in the event of any serious explosion inside.

The result was disturbing to the Japanese, as the shell passed through 76 mm (3.0 in) of armor and exploded in the port engine room.

In the latter, this meant that the side belt armor was continued below the waterline and beneath the torpedo bulge so the class would have a defense against underwater shells.

To ensure this, the Commander in Chief of the Kure Naval District directed that preparations for scuttling the ship be completed by 1 February.

The intention is to fill her hull with sand and gravel, tow her out to deep water near the entrance to Kure, open her sea cocks, and send her to the bottom.

[24][25] It was then towed from the bay on the 6th with the intention of bringing the battleship to the designated sinking spot, but were thwarted by a strong storm and returned.

Explosive "mines" were embarked: two 360 mm (14.2 in) shells were placed inside Tosa's double bottom, and two containers with 30 kg (66 lb) of Shimose powder in each were put into the engine room on the port side.

[25] The explosives were triggered on the 8th, but they failed, so a contingent was sent aboard Tosa on the 9th; they opened six Kingston valves in the engine room at about 01:25.

[25] Tosa was the tenth and final Japanese capital ship sunk or scrapped to comply with the naval treaty's stipulations.