While most naval wargamers seem to know the names and details of all the major warships and collect those models, gleefully, the lesser units are often little known, even if, as in the case of minesweepers, they have a vital role to play. Minesweepers of the Imperial Japanese Navy saw lots of combat and sea time in a variety of roles right from day one and were as much true fighting ships as any of the heavy units. During the Russo/Japanese war of 1904-05, the Japanese had quickly realized the value of minesweepers after they suffered some disastrous losses. From then on the IJN devoted a lot of time to mine warfare vessels, both for laying and sweeping.

W5 - W6 Type Sokai-Tei Minesweeper

For 'Fleet' work older torpedo boats and destroyers were used to sweep ahead of the heavy units, but it was obvious that this could only be a stop-gap solution and what was needed was a form of fast minesweeper able to perform a variety of roles including escort and small dispatch vessel. As it was envisaged, these ships could well be right up in the combat zone, vulnerable to enemy attack, the IJN planned their vessels to be well armed.

W1 and W5 classes

The W1 class were the first of the series planned in 1922 and all four were completed by 1925. They were trim little vessels with two unshielded 4.7 inch guns and a speed of 20 knots on a displacement of 615 tons. They had two funnels and looked like small destroyers, with which they had much in common, except for their twin shaft reciprocating machinery. To make them versatile in areas where supply might be difficult, they were designed to burn coal or oil. Trials were considered quite satisfactory and they could make 20 knots. These ships had pole masts. Although nominally a new class, W5 and W6 were almost identical to the previous four units. They had an extra knot of speed, slightly increased dimensions and a light tripod mast. These ships gave good service during the "China Incident" and there is a newsreel shot from the late 1930s in which you might spot one as it slides across the screen up close, its identification painted out, various positions surrounded by sandbags and the bridge hung with matting.

During WW II all six ships were extensively used, being considered equivalent to the British 'sloop' types. W6 was sunk by Dutch aircraft on the 26th of December 1941 during SE Asian opera-tions. W2 was mined near Java three months later. The others survived into the late war period in a variety of roles, but mostly escort duty, much of which was in Indonesian and Malaysian waters. By then, depth charges had become more important than minesweeping gear as the IJN struggled against the US submarine menace.

Only two survived to return to the Home Islands where minesweeping operations were being taken over by various auxiliaries and they were urgently needed as escorts.

W5 was sunk by the British submarine Terrapin near Sumatra on November 4th 1944 and W3 was a victim of the US submarine Parche northeast of Sendai on the 9th of April 1945. W1 was overwhelmed and sunk by aircraft of TF38 in Yamada Bay, near Harima, on the 10th of August 1945 just five days before the end of hostilities. The only survivor, W4 was captured at Singapore when the war ended and was scuttled by the British in 1946.

Missing Numbers

You will note that the above ships are numbered W1 to W6, yet the next class starts at W13. This is simply because old destroyers used as minesweepers, took up the numbers 7 to 12. They were discarded before WW II, which explains why a later class went backwards in designation number. W9 and W10 were Nara and Enoki. These were ex-Enoki class destroyers of 1917, converted in 1930 with armament reduced to two 4.7 inch guns and discarded in 1938. W7 and W8 were the ex Umikaze and Yamakaze respectively, both of the Umikaze class. They had a mixture of one 4.7 inch and four 80mm guns. No ships carried the numbers 11 or 12 after 1930 until the completion of the W7 class. The numbers 7 to 12 were carried by old 1904 built destroyers of the Asakaze class from 1926 until 1930. They were, in order of number, Isonami, Uranami, Ayanami, Minazuki, Nagatsuki, and Kikuzuki , all of which were armed with two 80mm.

W13 Class

These four units were built as a natural follow-on to the preceding vessels but although the alternative fuel and simple machinery was retained with twin shafts. They had a single funnel and a rather attractive clipper bow. Speed was 20 knots. Experience showed there was a need to lower topweight and this was done by reducing the size of the bridge and adding a ballast keel and internal ballast. My drawing shows the class after modification. A twin 13mm AA mount was placed amidships and a main armament of two single 4.7 inch guns was retained, with only the forward mount shielded.

The W13 class units saw much service along the coast of China. When WW II broke out they were active during the invasion of SE Asia where W13 and W14 were sunk by Dutch coastal batteries off Tarakan, Borneo, during the landings there. The other two soldiered on in the same waters, mostly as escorts, until W16 was mined near Makassar in the Celebes Group. W15 returned home to Japan where her armament and radar was altered. She was also involved in experiments with a Japanese submarine detection device known as the 'Y' locator. This used the Magnetic Anomaly principle, but was apparently a failure. She ran afoul of a mine laid by an American submarine and was run aground on Amani Island on March 5th 1945 in a severely damaged condition. She became a total loss.

The layout of this class was considered to be very satisfactory and became the standard for all other units to follow.

W17 Class

These were really modified ships of the W13 type that were altered during construction. There were only two units, but they had a much smaller bridge, lower topweight and a more traditional Japanese type bow shape than the clipper bow of the rest. This can be seen in my drawing. A twin 13mm AA mounting was placed amidships and main armament remained two 4.7 inch singles but the forward gun was shielded. The ships still kept reciprocating machinery and the ability to use alternative fuel type. They could make 19 to 20 knots. Ballast was added internally. Both were completed in 1936 and saw service in China as soon as they had worked up.

W7 and W17 Type

When war with the US commenced they were operating mostly around Korea, China and the Home Islands countering mines laid by American submarines. In 1944 they were given the ability to deal with magnetic mines. Their AA was upgraded with the addition of a twin 25mm before the bridge a single amidships and a twin aft. Hanging Lantern style radar was added before W18 was sunk by aircraft near Hainan in November of 1944. W17 continued on alone until severely damaged by a mine during the last few days of the war. It is possible this was one of the type deliberately sown to catch minesweepers. She was moored at Sasebo in a disabled condition when the Allies took over that port and having been considered not worth repairing for the postwar mine clearance effort, and was finally scrapped in 1947.

W7 Class

These six units filled the number gap left when the old destroyers were discarded. They were of later design than the higher-numbered W17 class. None the less they were very similar to the W13s and were completed between 1938 and 1939. A distinguishing feature was the bow, which matched that of the W17s.

They had two-shaft reciprocating machinery and could make 20 knots. The struggle in China was raging and war clouds were gathering over Europe adding impetus to the IJN decision to continue with this program. They were given a heavier gun armament in anticipa-tion of independent operation and to make them more useful in support of landing operations.

Their three shielded 4.7 inch gave them superior firepower to the three old 4 ich of the US Wickes class destroyers and compared favorably with many other destroyers they might encounter. Battle experience soon showed that the main enemies were submarines and mines, so eventually the aft gun was removed and depth charges increased from 18 to 36. The space freed up did, however, allow them to retain their sweeping gear. They had always carried a twin 25mm amidships in place of the 13mm of earlier classes and the AA was finally strengthened to 9 x 25mm on the survivors.

Units of this class took part in the landing operations that marked the start of the Pacific War, during which two were lost, W10 being sunk by USAAF aircraft defending Luzon, on the same day as the sinking of the Prince of Wales and Repulse. W9 was mined in February of 1942 near Ambon. No more were lost for two years but W7 was then sunk by the British submarine Storm, near the Andaman Islands in the Bay of Bengal. W11 was still in the south when she was sunk by US aircraft off Makassar on the 28th of March 1945 as was W12 when she fell victim to the US submarine Besugo off Sumbawa. The only survivor of the war was W8 which was captured at Soerabaya and then moved to Singapore, where she was scuttled off Malacca by the British on the same day as W4.

W19 Class

This group became the numerically largest class with 17 ships being completed. Many of the planned units had to be canceled due to conflicting priorities which also resulted in the numbers not running consecutively. Completed were W19 to W30, then W33, W34, W38, W39, and W41. Although planned through 1939 and 1940 it was February of 1941 before construction could start. Until now, all the minesweepers described had low angle 4.7 inch guns, however war lessons in Europe had shown the importance of AA and the design was altered to allow for this. The guns had a much more generous shield than that of the W7 class and there was a prominent canvas cover. As shown in my drawing, the later units also had a straight bow which aided in construction, but W19 to W24 had the same type of bow as the W7 class, making photographic identification of this class difficult, although the larger gun shields are distinctive. The ASW outfit was 12 to 18 depth charges and the class were to see much more service as escorts than as minesweepers. The twin 25mm amidships was later strengthened on all except W19 and W26, for a final total of nine, which seem to have been arranged as four twins and a single as shown in my drawing of the W7 class.

The construction of this class was held up by other projects and they straggled into service right through until July of 1944. Modifications followed those of the W7 class, which they so closely resembled, but their radius of action was greatly increased by converting some ballast tanks to carry fuel oil. This was particularly important as there main role was attempting to stem the assault by Allied submarines. W19 had completed by May 1941 and took part in the Philippines operations where she was severely damaged by air attack at Aparri, Luzon on the 10th of December 1941. The ship was beached but could not be recovered. W20 fell victim to the US submarine Trepang SE of Korea on the 4th of May 1945. W21 completed in June of 1942 and served mostly in Chinese and Korean waters, being finally captured at Tsingtao at the end of the War. After a period on Repatriation Service, she was awarded to the USA as war reparations but the USN had no use for her and she was scrapped after October of 1947. W22 was completed in mid 1942 and sank after striking a mine near Palau. W23 was completed in March of 1943 and was eventually handed to the Soviet Union at Nakhodka in 1947 after a spell with the Allied Minesweeping Service.

W24 completed early in 1943 and was finally sunk by aircraft of TF38 near Omasaki on the 15th of July 1945. W25 saw only 16 months of service, being completed in late April of 1943 and sunk by aircraft of TF58 near Ogasawara Gunto on the 4th of July 1944. W26 had a short life, being completed in March of 1943 but caught at Rabaul by US Naval aircraft, probably from Saratoga in November. She was unrepaired when finally sunk by another air attack in February 1944.

W27 saw almost two years service from her completion on the 31st of July 1943 until she was the loser in an encounter with the US submarine Runner off Todo Point, Iwate Prefecture on the 10th of July 1945. W28 completed in June of 1943 and became a victim of the submarine Jack NW of the Celebes on the 29th of August 1944. W29 was mined off Kinzurasaki on the 7th of May 1945, having completed in October of 1943. W30 was another victim of TF38 aircraft on November 11th 1944. She had only entered service in February of the same year.

W31 to W32 were canceled. W33 was completed on the 31st of July 1943 and destroyed by an American carrier strike on shipping in the Onagawa Bay area on the 9th of August 1945 during the closing days of the war. W34 saw 12 months' service, being completed on May 29th 1944 and sunk on the 21st of May 1945 off Kepulauan by the US submarine Chub. W35 to W37 were canceled. W38 was a late war unit completed on June 10th 1944 but was sunk SW of Taiwan on the 20th of November the same year by the submarine Atule. W39 was another late unit, completing on the 31st of May 1944 and being sunk on the 20th of July 1945 by the submarine Threadfin off Shushi Island in South Korean waters.

W40 was canceled and W41 became the last of the class to be completed, entering service on the 17th of July 1944. She was another victim of TF38 aircraft being severely damaged and beached on Taiwan on the 4th of January 1945. She could not be repaired and was eventually abandoned.

Summary

With 35 units completed, the minesweeping sloops of the IJN were an important part of the escort force once war broke out. During the start of the US submarine offensive against Japan, these ships were forced to bear the brunt of escort duty, for which they were well suited. In general performance they can be seen to have performed a similar role to the Prewar sloop designs of the British Navy and like them progressed from low angle main armament to high angle.

Similarly, antisubmarine armament became extremely important as demand for them to perform escort roles rather than their designed function, grew. Their speed of around 20 knots was quite sufficient for their role. Some sources state that the W13, W7, and W17 classes had turbine engines but the majority of evidence leads me to the conclusion that two shafts, two boilers and VTE reciprocating machinery was retained. Progressive development of the classes was limited to minor improvements in layout. Standardization would have certainly made maintenance and training easier. The only significant machinery difference seems to be that the W1 and W5 classes had three boilers, not two.

Because of their dual capacity, these ships were considered very valuable, but of course the very fact of them being drawn off on to other duties meant that when the extensive US mining program commenced, they were not available to help. Aircraft and submarine-laid mines became a nightmare for Japanese merchant shipping and if other escorts had been available, there is no doubt these ships could have had a busy war just carrying out their intended role. They commenced the Pacific War sweeping ahead of landing forces, that they had also escorted but after 1942 there was no need for offensive minesweeping.

The other class, W101 to W102, which were ex-British Bangor class ships captured at Singapore, have been covered in a separate article. The Wa-1 class were ships of basically diesel-engined commercial fishing design with an 80mm gun, some light flak and a few depth charges. Despite their small size they were sent far afield, including the Solomons and SE Asia, although most were used in home waters, where many were captured at the end of the war and were used on repatriation and mine clearance duties. The Wa-101s were captured ex-Dutch vessels used in Indonesian waters.
BT