Accentor class minesweeper
USS Accentor
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| Class overview | |
|---|---|
| Built: | 1941–1942 |
| In commission: | 1942–1946 |
| Completed: | 70 |
| General characteristics | |
| Displacement: | 185–205 tons |
| Length: | 97 ft 1 in (29.59 m)–98 ft 5 in (30.00 m) |
| Beam: | 21 ft (6.4 m)–23 ft 7 in (7.19 m) |
| Draft: | 8 ft 11 in (2.72 m)–10 ft 8 in (3.25 m) |
| Propulsion: | Diesel engine, 400 hp (300 kW) |
| Speed: | 10 knots (19 km/h) |
| Complement: | 17 |
| Armament: | 2 × .50 cal. M2 Browning machine guns |
In World War II, the United States Navy needed a vessel that could consistently locate mines in [foreign or domestic?] or littoral waters. Littoral waters are found between the shore line and waters 60 meters deep. The Accentor-class minesweeper (sometimes called the Accentor/Acme-class minesweeper) was developed for this task. This class of minesweeper was named after the Accentor bird, Prunella modularis. This bird is endemic to Europe, Asia, and North Africa which is the area that World War II occurred. The bird is a drab brown and gray color and is in the same family as warblers and thrushes. The Accentor-class mine sweeper was designed for the sweeping of mines in harbors, bays, and other littoral waters. The Accentor-class minesweeper had a wooden hull for three reasons. The first was that some of the mines that the Accentor-class minesweeper was trying to detect were detonated by a copper wire coming out of the top of the mine that is used to detect the magnetic field that is produced by the metal hulls of most ships; when the wire senses a magnetic field, it detonates the mine. Minesweepers use wooden hulls because wood is a non-magnetic material, unlike steel, and would not set off this type of mine. The second is that wooden hulls were lighter than metal hulls. This caused them to float higher in the water, which made them displace less water and have a smaller pressure wave, so pressure mines would not be set off by the movement of the ship. Lastly, due to the ship floating higher in the water, contact mines were not effective because they were often around 20 feet below the surface of the water, and the draft of this class of ship was between 8 feet 11 inches and 10 feet 8 inches. Typically, the Accentor-class minesweepers were armed with a pair of .50 caliber machine guns for protection. Rather than creating new minesweeping vessels, forty-five wooden-hulled fishing boats were converted into Accentor-class minesweepers. This saved the Navy both time and money. Since these converted fishing boats were not all the same, their specifications do vary a bit. The converted fishing boats had a displacement from 165 to 270 tons of water. They had speeds from 8.5 up to 14 knots and crews from as small as 15 up to 50.
In World War II the Accentor-class minesweeper was used to find five different types of mines. First is naval mines. This type of mine was covered in pressure sensors called detonating horns that detonated when a ship's pressure wave hits it. Second is the army mine. Army mines were remotely detonated by troops on land. The next is the antenna mine that has a copper wire to detect the magnetic field of a passing ship. Then there was leon mine which has a battery-powered motor that moves it up and down. It will detonate when it hits a ship. Lastly there are sonic mines that are detonated by the noise made by the engines of a passing ship. To sweep for these mines, the Accentor-class minesweepers used a complicated system that consisted of about 150 feet of wire line, a depressor, a cutter, an otter, and a float. The float sits on the surface of the water and is used to pull the end of the wire line out to the side of the ship to increase the area that the mine sweeper could sweep and not just have the system drag behind the ship. It uses a fixed rudder to set the angle that the float is from the ship, and since the float is on the end of the line this is also the angle that the line is from the ship. The float is connected to the otter by the line. The otter is like a metal kite that sweeps thirty feet under water. Next on the line is the cutter which cuts the cable that connects the mine to the mine anchor. Next is the depressor. The depressor was used to pull the line down to thirty feet underwater so that the mines would get caught on the line and the forward motion of the ship would drag the mine to the cutter. This was attached to the minesweeper by a pulley and winch system that allowed the ship to control the distance that the otter was from the ship. One of the problems with the Accentor-class minesweeper is that its small size made it difficult to get across oceans unless the weather was good. The minesweeper could get across an ocean, but it had to be scheduled around bad weather. The Accentor-class minesweepers were primarily meant to be used to locate mines that were in Allied water. This mines could include mines placed by Allied military for protecting harbors. Mines were placed so that the enemy was denied access to Allied coastal waters and harbors. This is called defensive mining. Offensive mining is used to close the coast of an enemy and the enemy’s harbors to their ships.
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