W-1-class minesweeper

The W1 class minesweeper (第一号型掃海艇,) was a class of minesweepers of the Imperial Japanese Navy (IJN), serving during the 1930s and World War II. 6 vessels were built in 1922–29 under the Eight-eight fleet plan. They have two sub-classes, this article handles them collectively.

Background
In 1920, the IJN made an Eighty-eight Fleet Plan which would provide them with eight battleships and eight battle cruisers. However, they did not forget the Hatsuse and Yashima, which had struck naval mines during the Russo-Japanese War and the IJN was afraid of this event occurring once again.

In the IJN, destroyers undertook minesweeping operations but could also lay their own minefields. As a result, the fleet wanted a brand-new minesweeper which could follow their battleships into an action and this would become the No.1-class.

No.1 class

 * Project number I1. 4 vessels were built in 1922-1925. W-4 was behind with the laid down by the Washington Naval Treaty.

No.5 class

 * Project number I2. 2 vessels were built in 1928-1929. Improved model of the No.1-class. About their appearance, foremast was changed to tripod type.