Talk:Naval mine
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Double paravane sweep?
I have never heard of this being used. It seems like it would make the risk far worse for the sweeper with no gain, compared to simply having a single paravane and twice the cabel length to cover the same area. When sweeping you either start on "safe" water and work your way into the minefield without ever exposing the sweeper, or if in a real hurry to clear a path, you sweep a single line through the minefield and then you keep the sweeper in water you know are clear while enlarging it. A double paravane sweep is a lot of extra work and no gain in both cases. It would also make it harder to cut the sweeper free, as the crew would have to remove several extra wires to clear the sweeper in the case of an attack.
-Pehrs
The mining threat
The first actions of the naval campaign started the day that war was declared. Royal Navy vessels dredged up and cut German transatlantic communication cables, forcing the Germans to communicate to their interests in the Americas by less secure means for the rest of the war.
The U-boat fleet, which was to dominate so much of the battle of the Atlantic, was very small at the beginning of the war and much of the early action by German forces involved mining convoy routes and ports around Britain. Initially, contact mines were employed, which meant that a ship had to physically strike one of the mines in order to detonate it. Contact mines are usually suspended on the end of a cable just below the surface of the water and laid by ship or submarine. By the beginning of World War II most nations had also developed mines that could be dropped from aircraft, making it practicable to lay them in enemy harbours (although they simply floated on the surface). The use of dredging and nets was effective against this type of mine, but nonetheless was time-consuming, and involved the closing of harbors while it was completed.
Into this arena came a new mine threat. Most contact mines leave holes in ship's hulls, but some ships surviving mine blasts were limping back to port with buckled plates, popped rivets, and broken backs. This appeared to be due to a new type of mine that was detonating at a distance from the ships, and doing the damage with the shockwave of the explosion.
These mines were devastating; often ships that had successfully run the gauntlet of the Atlantic crossing were destroyed entering freshly mineswept harbors on Britain's coast. More shipping was now being lost than could be replaced, and Churchill ordered that the recovery, intact, of one of these new mines was to be given highest priority.
Then the British experienced a stroke of luck in November 1939. A German mine was dropped from an aircraft laying mines onto mud flats in the Thames estuary, well above the waterline. As if this was not sufficiently good fortune, the land happened to belong to the army, and a base, including men and workshops were close at hand.
Experts were quickly dispatched from London to investigate the mine. They had some idea by this time that the mines used magnetic sensors, so they had everyone remove all metal, including their buttons, and made new tools out of non-magnetic brass. They then safed the mine and rushed it to labs at Portsmouth, where scientists discovered a new type of arming mechanism inside.
The arming mechanism had a sensitivity level that could be set, and the units on the scale were milligauss. Gauss is a measurement for the strength of a magnetic field, and so they knew why it went off before coming into contact with the ship. Using the detector from the mine, they were able to study the effect of a ship passing over it. A ship, or any large ferrous object passing through the earth's magnetic field will concentrate the field at that point. The detector from the mine measured this effect, and was designed to go off at the mid-point of the ship passing overhead.
From this crucial data, methods were developed to clear the mines. Early methods included the use of large electromagnets dragged behind ships, or on the undersides of low-flying aircraft (a number of older bombers like the Vickers Wellington were used for this purpose). However both of these methods had the disadvantage of "sweeping" only a small strip at a time. A better solution was found in the form of electrical cables dragged behind ships, passing a large current through the seawater. This induced a huge magnetic field and swept the entire area between the two ships. The older methods continued to be used in smaller areas; the Suez Canal continued to be swept by aircraft, for instance.
While these methods were useful for clearing mines from local ports, they were of little or no use for enemy controlled areas. These were typically visited by warships only, and the majority of the fleet then underwent a massive de-gaussing process, where their magnetic fields were reduced to such a degree that it was no longer "noticed" by the mines. This started in late 1939, and by 1940 British warships were largely immune for the few months at a time until they once again built up a field. Many of the boats that sailed to Dunkirk were de-gaussed in a marathon four-day effort by hard-pressed de-gaussing stations.
The Germans had also developed a pressure-activated mine and planned to deploy it as well, but they saved it for later use when it became clear the British had beaten the magnetic system. They were then sown across likely invasion areas off the coast of France. This system had the disadvantage of requiring a periodic resetting of the trigger mechanism, so they were attached to chains and cables so they could be pulled to the surface and reset. Unlike the contact mine, however, in this case the mine lay on the ocean floor, and the cable ran to a float on the surface.
In 1944 General Erwin Rommel timed the resetting so that the mines would be at their best effectiveness during late April and into May - the best time for an allied invasion of France during the early summer. In June they were getting past the point of effectiveness and he ordered them pulled in for maintenance. The allies launched D-Day on June 6th, and the mines could not be replaced until it was too late.
Minesweeping
This article has more details about minesweepers and minehunters than the actual articles about minesweepers and minehunters. Maybe we should move the information, and have the countermeasures section be shortened. - LtNOWIS 18:29, 31 Oct 2004 (UTC)
Mine models
This page contains information on a variety of different mines. Perhaps this information should be broken out into individual pages for each significant mine model? Further; a top page listing the various models, including foreign models. I suggest this because the M-08 mine appears in a few pages regarding Operation Praying Mantis and the ships involved, and it seems appropriate to make such a page (I'm about to do this). Mine warfare is an often overlooked aspect of naval warfare, yet it is responsible for casualties to more USN ships than any other weapon type since World War II. It seems appropriate that more effort should be devoted to this area of naval weapons, and thus more breakout of the information into appropriate subpages. --Gcashman 22:14, 8 Apr 2005 (UTC)