# W-1-class minesweeper

The W1 class minesweeper (第一号型掃海艇,, Dai Ichi Gō-gata Sōkaitei) 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 developed an Eight-eight Fleet Plan which would provide them with eight modern battleships and eight battle cruisers. However, they did not forget the Hatsuse and Yashima, which had struck naval mines during the Russo-Japanese War; afraid of such events occurring again, the IJN also ordered the No.1-class of purpose-built minesweepers, to replace converted old destroyers in the minesweeping role.
As the IJN anticipated its minesweepers to operate in front of the main battle fleet, and therefore to encounter enemy warships, the No.1-class were more heavily armed than minesweepers of other nations, with each ship mounting two 120 mm (4.7 in) L/45 naval guns. In addition each ship could carry 50 naval mines, making them multi-purpose vessels visually resembling small destroyers.

## Ships in classes
### 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.
| Ship | Builder | Laid down | Launched | Completed | Fate |
| W-1 | Harima Zōsen | 10 May 1922 | 6 March 1923 | 30 June 1923 | Sunk by air raid at Yamada Bay on 10 August 1945; removed from naval ship list on 15 September 1945. |
| W-2 | Mitsui, Tama Shipyard | 13 April 1922 | 17 March 1923 | 30 June 1923 | Sunk by friendly torpedo by Mogami or Mikuma at Bantam Bay during the Battle of Sunda Strait on 1 March 1942; removed from naval ship list on 30 November 1945. |
| W-3 | Ōsaka Iron Works | | 29 March 1923 | 30 June 1923 | Sunk by USS Parche at Ōfunato Bay on 9 April 1945; removed from naval ship list on 10 May 1945. |
| W-4 | Sasebo Naval Arsenal | 1 December 1923 | 24 April 1924 | 29 April 1925 | Survived war; scuttled by Royal Navy off Singapore on 11 July 1946; removed from naval ship list on 10 August 1946. |

### 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.
| Ship | Builder | Laid down | Launched | Completed | Fate |
| W-5 | Mitsui, Tama Shipyard | 25 March 1928 | 30 October 1928 | 25 February 1929 | Sunk by HMS Terrapin at Strait of Malacca 33°44′N 99°50′E﻿ / ﻿33.733°N 99.833°E﻿ / 33.733; 99.833 on 4 November 1944; removed from naval ship list on 10 March 1945. |
| W-6 | Ōsaka Iron Works | 10 March 1928 | 29 October 1928 | 25 February 1929 | Sunk by air raid off Kuching 01°34′N 110°21′E﻿ / ﻿1.567°N 110.350°E﻿ / 1.567; 110.350 on 26 December 1941; removed from naval ship list on 10 January 1942. |

## Photos

* 1st Minesweeping Squadron W-3 and W-2 in front
* W-4 in July 1930
* W-5 in the 1930s (after the Tomozuru-Incident)
* W-6 on 28 May 1933

## Footnotes

* ↑ Minesweeper W-1 (第一号掃海艇, Dai 1 Gō Sōkaitei). The same shall apply hereinafter.
* ↑ In the neighborhood of spot, many parts of the Type 93 torpedo were discovered. The Japanese destroyers which participated in Battle of Sunda Strait were not equipped with Type 93 torpedo.