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.

W-3 in 1923
Class overview
Name	W-1-class minesweeper
Builders	Sasebo Naval Arsenal Harima Zōsen Mitsui Bussan Ōsaka Iron Works
Operators	Imperial Japanese Navy
Succeeded by	W-13 class
Subclasses	W-1 class (Project Number I1) W-5 class (Project Number I2)
Cost	700,000 JPY (in 1920)
Built	1922–1929
In commission	1923–1946
Planned	6
Completed	6
Lost	5
Scrapped	1
General characteristics W-1-class
Type	Minesweeper
Displacement	600 long tons (610 t) standard
Length	76.20 m (250 ft 0 in) overall
Beam	8.03 m (26 ft 4 in)
Draught	2.29 m (7 ft 6 in)
Installed power	3 × Kampon coal-fired boilers 4,000 shp (3,000 kW)
Propulsion	2 shafts, 2 × triple-expansion steam engines
Speed	20.0 knots (37.0 km/h; 23.0 mph)
Range	2,000 nmi (3,700 km; 2,300 mi) at 10 knots (19 km/h; 12 mph)
Complement	97
Armament	2 × 120 mm (4.7 in) L/45 naval guns 1 × 76.2 mm (3.00 in) L/40 AA gun 18 × depth charges 2 × Type 81 depth charge projectors 1 × paravane or 50 × Mk.5 naval mines
General characteristics W-5-class (differences only)
Displacement	620 long tons (630 t) standard
Length	77.00 m (252 ft 7 in) overall
Beam	8.25 m (27 ft 1 in)
Draught	2.25 m (7 ft 5 in)
Complement	91
Armament	2 × paravanes or 50 × Mk.5 naval mines

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 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 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

Bibliography

• Jentschura, Hansgeorg; Jung, Dieter & Mickel, Peter (1977). Warships of the Imperial Japanese Navy, 1869–1945. Annapolis, Maryland: United States Naval Institute. ISBN 0-87021-893-X.
• Ships of the World special issue Vol.45, Escort Vessels of the Imperial Japanese Navy, "Kaijinsha"., (Japan), February 1996
• The Maru Special, Japanese Naval Vessels No.50, Japanese minesweepers and landing ships, "Ushio Shobō". (Japan), April 1981