Destroyer minesweeper


Destroyer minesweeper was a designation given by the United States Navy to a series of destroyers that were converted into high-speed ocean-going minesweepers for service during World War II. The hull classification symbol for this type of ship was "DMS." Forty-two ships were so converted, beginning with, converted to DMS-1 in late 1940, and ending with, converted to DMS-42 in mid-1945. The type is now obsolete, its function having been taken over by purpose-built ships, designated as "minesweeper " with the hull classification symbol MMD.
The s and s chosen for conversion were obsolete four-stack destroyers built in 1918 that still had usable power plants; they were nicknamed "four-pipers" on account of their four smokestacks. Although the full conversion process to minesweepers for the original 17 Wickes and Clemson-class destroyers began in October—November 1940, it was not completed for all 17 until around mid-1942. When they were fully converted from destroyers to destroyer minesweepers, the number 4 boiler, the fourth stack from the bow, and the torpedo tubes were removed, the depth charge racks repositioned forward from the stern and angled outboard, and the stern modified to support sweep gear: davits, winch, paravanes, and kites. Two 60-kilowatt turbo-generators replaced the three original 25-kilowatt generators to improve capability for sweeping magnetic and acoustic mines.
The majority of mines left by the Japanese in the Pacific were contact mines which were usually moored and could be removed by a paravane. The Japanese never created their own magnetic or pressure mines, though they captured a very limited number of magnetic mines from the British, which they laid off Balikpapan in 1945. Magnetic mines in the European theater were usually disabled by towing a magnetized cable, often swept by wooden-hulled ships, but occasionally swept by iron-clad ships that were degaussed to mask their magnetic properties. Minesweeping in the Pacific theater in World War II consisted primarily in the use of sweep wires suspended between paravanes and kites, particularly among destroyer minesweepers.

''Wickes''-class minesweepers

Conversion of the initial seventeen ships, begun in October and November 1940, included eight and nine s.
Following are the Wickes-class destroyers that were converted to minesweepers and subsequently designated DMS-1 to DMS-8:

  • ''Clemson''-class minesweepers

In 1941 ten more destroyers were converted, and designated DMS-9 to DMS-18. This time nine were Clemson-class ships and only DM-18 came from the Wickes class.
Image:USS Hovey off the Mare Island Naval Shipyard on 7 June 1942.jpg|upright=1.4|right|thumb|Minesweeper USS Hovey, June 1942, pre-conversion, 4 smokestacks, and 4" guns front and rear, around 8 x 50 cal AA guns
The Clemson-class destroyer USS Hovey, is shown at right, not fully converted, in June 1942, still with four smokestacks. The fully converted USS Hovey is shown below right, with three smokestacks, a squared off stern with two cranes visible for hauling minesweeping gear, and three guns visible fore, midship, and one on the aft deckhouse.
The nine converted Clemson-class destroyers and one Wickes-class destroyer completed by November 1940 are listed below:
At first the ships above retained their initial four 4 inch guns for defense. In 1942 they were scheduled to get 3"/50 caliber dual purpose guns as they needed to be prepared to face air attack in WWII. By 1944, their armament included two or three 3"/50 caliber dual purpose guns and twin power operated Bofors guns, which were highly effective against enemy aircraft. Their dual purpose 3 inch guns could be used against enemy shore batteries, to fire on surfaced submarines, and as effective anti-aircraft weapons. The destroyer minesweepers usually lost all four of their original four 4 inch guns when they received their 3"/50 caliber and Bofors guns, but they retained a significantly improved capability against Japanese enemy aircraft including kamikazes which many of these ships faced between January and May 1945.

Fates of WWII destroyer minesweepers

The USS Wasmuth, after spending much of her WWII career sweeping and escorting ships in the Aleutians, was sunk when a gale in Alaskan waters dislodged two of her depth charges that exploded by her hull in December 1942. The threat of a depth charge dislodging and exploding during a storm was a topic covered by Herman Wouk in the climax to his novel The Caine Mutiny. The executive officer Steve Maryk urged Captain Queeg to set the depth charges on destroyer minesweeper Caine on "safe" during a storm, though Queeg was enraged when he discovered this had been done earlier without his knowledge or permission.
The Perry, a Wickes-class destroyer in the list above, was sunk by naval mines on September 13, 1944, off Palau while she was involved in sweeping duties. Records indicate she may have been the only destroyer minesweeper sunk by a naval mine while sweeping in WWII. The Wickes-class minesweeper Dorsey had to be destroyed after she ran aground off Okinawa from Typhoon Louise in October 1945, and the Wickes-class Lamberton was run aground with minor damage in the same storm. In the Battle of Lingayen Gulf, from January 3–7, 1945, three Clemson-class destroyer minesweepers listed above, the Hovey, the Long, and the Palmer, were sunk primarily by kamikazes and the Southard was lightly damaged by a kamikaze, though she later had to be destroyed after running aground at Okinawa during Typhoon Louise in October 1945. The Hopkins survived the Battle of Lingayen Gulf off Luzon unscathed, though four of the seven ships in Hopkins's minesweeping Task Force 77.6, Unit 1 were hit. The destroyer minesweeper Chandler initially rescued the survivors of minesweepers Hovey and Long as well as a few of the survivors of Clemson-class destroyer Brooks at Lingayen on January 7, 1945 and served out WWII without damage from combat. The Dorsey, the Hogan, the Hamilton, and the Howard escaped damage in the Battle of Lingayen Gulf, the most dangerous battle of the war for Clemson-class destroyer minesweepers, and survived the war. Around fifty American naval vessels, five destroyer minesweepers among them, were lost or damaged at Lingayen Gulf in the first two weeks of 1945.
Full assault by Japanese torpedo planes, bombers, and kamikazes against the semi-isolated destroyer minesweepers in the difficult waters of Lingayen Gulf proved too much for their antiaircraft capabilities when isolated from the screening that could be provided by more heavily armed destroyers and battleships. As the Naval historian Samuel Eliot Morison noted with respect to the destroyer minesweepers at the Battle of Lingayen Gulf, the “Japanese seemed to pick on minecraft because they were usually isolated and had no good antiaircraft support”. Nonetheless, only one destroyer minesweeper, the highly upgraded Gleaves-class Emmons, was sunk in combat by kamikazes after Lingayen Gulf, and she was struck a remarkable total of five times at the Battle of Okinawa before sinking. The Navy itself acknowledged the daunting task faced by minesweepers in defending against enemy aircraft with relatively light armament, as the commendation for the Emmons presented by the Secretary of the Navy acknowledged that she was "lightly armed and highly vulnerable while operating in dangerous mined waters". The Emmons had significantly more anti-aircraft guns than the Wickes and Clemson-class destroyer minesweepers that battled kamikazes and Japanese escort planes at Lingayen Gulf only three months earlier.
Few destroyer minesweepers had been lost in combat prior to the Battle of Lingayen Gulf, as their primary and essential function was to sweep mines or hunt the occasional submarine, not to engage in ship to ship combat, particularly since they lacked torpedoes after their full conversion to minesweepers in 1942. Once their minesweeping duties were completed, they were usually vacated to another area, or performed escort duties protecting supply vessels from enemy aircraft and submarines. The Battle of Okinawa would prove to be even more disastrous for the destroyer minesweeper fleet than Lingayen Gulf, with roughly seven times more Japanese aircraft engaged as kamikazes.

Minesweeping methods

WWII Japan never developed its own magnetic or pressure mines, so for those destroyer minesweepers in the Pacific, mines were usually cut from their mooring by a paravane, shown at left, extended by a sweep line from the rear or sides of a minesweeper, assisted by the use of sonar to locate the submerged mines. Sonar could operate at a few thousand hertz to around ten thousand hertz for shallower mine location, but sonar frequencies as high as 24 thousand hertz were routinely used to track submarines at depth. WWII mine location sonar in the Pacific in WWII was one of the first true search sonars and employed frequency modulation. Its range, in perfect conditions, could not exceed 800 yards or 730 meters, which was inadequate for purposes other than locating and plotting minefields. The sonar had a Plan Position Indicator, similar to those on high quality modern radar, which showed mines as bright green "pears". The sonar also conveniently made a sound audible to the minesweeping crewman, when a mine was swept by its beam, a clear ringing note the mine crews dubbed "hell's bells."
Paravanes could be towed from one or both sides of a ship's stern, or occasionally bow, though destroyer minesweepers nearly always towed them from the stern. The sweep line caught the moored mine's cable below the surface, causing the paravane to slide to the mine and have its blades cut the mine from its mooring cable. The mine then floated to the top and was usually destroyed or sometimes sunk by gunfire from an American naval ship. In some applications, cutting devices were placed on the sweep line itself, or the sweep line could be serrated to do the cutting, but paravanes with blades were used much more frequently by American ships to cut mooring cables in the Pacific in WWII. In most configurations, a kite, basically an unbladed paravane, could be used near the ship to maintain the sweep wire parallel to the bottom at a specified distance from the paravane. The paravane operator would need to know the depth of the moored mines to set the proper depth of the paravane and kite, and could use sonar for this purpose.
Minesweeping ships would often travel side by side in formation to sweep a larger channel. Large winches and two large davits which looked like cranes on each side of the stern of minesweepers were used to haul minesweeping gear. Acoustic mines were destroyed by sound generators that imitated the sound frequencies of a passing ship, and electrical mines, though rarely used by the Japanese, could be destroyed by an electrical device or cable passed close to the mine causing it to detonate. Ship sonar was used as an invaluable tool in locating mines in WWII. More sophisticated pressure mines were used by Germany in the Atlantic but were not frequent and their use was delayed by the Germans until 1944 at the Battle of Normandy. Pressure mines were activated by the increase in water pressure under a moving vessel, and had to be swept using a towed hulk large enough to produce the required pressure surge. Markers in the form of buoys were often used to mark mineswept lanes where transport ships or landing craft could find safe passage to beach heads or other destinations. Buoys were usually used to mark the end of a mine sweep cable floated directly above the paravane, and could be particularly helpful when minesweepers were sweeping in formation.