Neither Great Britain nor the United States had devoted significant resources to mine warfare. The Royal Navy had adhered to the fleet sweeper design and hastily commissioned the somewhat inadequate Bangor-class minesweepers in 1940 to replace the unsuitable Halycon fleet sweepers. The new challenges posed by mine warfare soon required design changes. The German prewar designs proved inadequate and too complicated for mass production. Like the Bangors, they soon turned out to be too cramped to accommodate the extra sweep gear for use against influence mines. New minesweeper designs also required more powerful auxiliary engines that could produce the necessary current for the magnetic-influence sweeping gear.
The Germans responded by building the 1940- and 1943-type minesweepers. Although similar in appearance to the 1935-type, those vessels were simplified to the point where their sections could be largely prefabricated by specialized yards and assembled by others. The turbines were substituted by coal-fired, triple-expansion engines for cost reasons and to conserve the navy's oil fuel stocks. Otherwise, except for the improved sweeping facilities, added antiaircraft armament, and minor details, the layout of the German minesweepers remained essentially unchanged.
The British substituted for their Bangor-class ships the larger, 1,200 ton, Algerine-class vessels, of which nearly 100 were built. The concept was a return to the fleet sweeper, and with their armament of 1 x 4-inch gun, 4 x 40-mm guns, and 92 depth charges, the Algerines easily outclassed the smaller Flower-class corvettes in their escort role.
The United States woke up late to the Japanese mine threat, which turned out to be a minor irritant at most. Many U.S. minesweepers subsequently saw heavy action in the Normandy landings and in the preparation for them. Apart from the 1918-vintage Bird-class minesweeper, the U.S. Navy commissioned nearly 200 minesweepers. Most were of three main types: the big Raven- and Auk-classes; two-funneled diesel vessels of 810 and 890 tons, respectively, with a speed of 18 knots and one or two 3-inch guns; and the diesel-powered Admirable-class of 650 tons and 15 knots.
For economic reasons and for inshore sweeping, all navies took to building motor minesweepers as a cheap alternative to the fully fledged minesweepers. These boats, produced by the hundreds, ranged from the British 80 ft motor launches and the German 120 ft Räumboote (minesweepers) to the somewhat understated U.S. yard minesweepers (YMS) that, at 136 ft in length, displaced 215 tons. Nearly all of the motor minesweepers, except the very smallest, eventually assumed duties beyond inshore or harbor sweeping.
The explosive growth of the minesweeping forces in World War II contrasted with that of the dedicated minelaying forces. As in the years from 1914 to 1918, most navies were content to rely on converted civilian vessels or regular combatants, such as destroyers, submarines, and patrol boats, for the bulk of their minelaying activities. Very few purpose-designed minelayers, such as the British Abdiel-class, were built before and during the war. At 37 knots, these 4,000 ton vessels were exceptionally fast. The advent of large-scale aerial offensive mining, however, rendered them largely obsolete. The Abdiels eventually ended up as fast blockade-runners to Malta and elsewhere. Dirk Steffen
Gardiner, Robert, ed. Conway's History of the Ship: The Eclipse of the Big Gun. London: Conway Maritime Press, 1992.; Gröner, Erich, ed. Die deutschen Kriegsschiffe, 1815–1945. Vols. 3 and 4. Koblenz, Germany: Bernard and Graefe Verlag, 1985–1986.; Lott, Arnold S. Most Dangerous Sea: A History of Mine Warfare and an Account of U.S. Navy Mine Warfare Operations in World War II and Korea. Annapolis, MD: Naval Institute Press, 1959.