Dreadnought Battleship: Tosa Class

[Brian James]

Lieutenant General Nagamura Kiyozo pictured as he watches the uncompleted Lead Ship, Dreadnought Battleship Tosa being towed from Kure Naval Arsenal on January 31st 1925...Lead Ship of the Tosa Class of two 39,900-long ton (40,540 ton) ships. The Battleships would have been armed with ten 16.1 inch 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 February 9th 1925...One of the tests conducted around this time involved a 16.0 inch gun firing a shell at Tosa. It fell about 82 ft short of the ship, but continued through the water and struck the ship near frame 228, 11 ft below the designed waterline. The result was disturbing, as the shell was able to pass through the 3.0 inch armour and explode in the port engine room. As a result, 3,000 long tons (3,048 t) of water was let in, and Tosa's list was increased from 4° 53' to 10° 06'...Results of the tests on Tosa were subsequently used in the refitting and reconstruction of existing warships. Lessons learned were also incorporated into the designs of the two Yamato Class super-Battleships ten years later. In the latter, this meant that the side belt armour was continued below the waterline and beneath the torpedo bulge so that the Class would have a defense against underwater shells.

[Brian James]

The uncompleted Dreadnought Battleship Tosa pictured being towed from Mitsubishi Shipyards at Nagasaki on August 1st 1922...Two ships were launched in late 1921, but the first ship, Tosa, was cancelled in accordance with the terms of the Washington Naval Treaty before it could be completed, and was used in experiments testing the effectiveness of its armour scheme before being scuttled in the Bungo Channel on February 9th 1925.. The hull of the second ship, Kaga, was converted into an Aircraft Carrier. The Tosa Class ships were intended to be armed with a main battery of ten 16.1 inch 45-calibre guns in five twin turrets, four of which were superfiring fore and aft. Numbered one through five from front to rear, the hydraulically powered turrets had an elevation range of −2 to +35 degrees. The rate of fire for the guns was around two rounds per minute. The ships were designed to carry 90 rounds per gun, although space was available for 110.

[Brian James]

Launch day for Lead Ship, Dreadnought Battleship Tosa pictured on the ways at Mitsubishi Shipyard, Nagasaki on December 18th 1921...Construction began in 1920, but the 1922 Washington Naval Treaty intervened, mandating the cancellation of all capital ships being built. Work stopped on the two Tosa-Class Battleships on February 5th 1922. After being stricken on April 1st 1924, her guns were turned over to the Imperial Japanese Army for use as coastal artillery; two of her main-gun turrets were installed on Tsushima Island and near Busan, Korea. The rest of her guns were placed in reserve and ultimately scrapped in 1943. Tosa's incomplete hull was used to test her armour scheme against long-range naval gunfire, aerial bombs, mines and torpedoes. Two of the shells fired at her fell short, but deeply penetrated her hull through the thin armour of the torpedo bulge below the waterline armour belt. This sparked an interest in optimizing underwater performance of Japanese shells that culminated in production of the Type 91 armour-piercing shell. Conversely, the IJN took measures to defend against shells of this type when reconstructing its existing Battleships during the 1930s, as well as in the designs of the Yamato-Class Battleships and the Heavy Cruisers of the Mogami and Tone classes. Tosa's torpedo defense system proved able to defeat 440 lb torpedo warheads, but not larger 770 lb ones. After the conclusion of the tests, the ship was scuttled by opening her Kingston valves on February 9th 1925 in 2,130 ft of water in the Bungo Channel after the demolition charges failed to detonate.