Contact mines are anchored to the ocean floor with cables that keep them floating just beneath the surface. To neutralize them, the mooring cable must first be severed, to allow the mine to bob up and become visible. Minesweepers drag along a steel wire that ends with a torpedo-shaped floater. Not far from the floater is a steel frame with angled fins, called the "otter" that keeps the wire under water at the proper depth as the minesweeper moves along. The wire is fitted with cutters. When a mine cable touches the wire, it slides along it until it hits a cutter. As the cable breaks, the mine is freed and bobs up to the surface. It must then be destroyed by firing at it with guns or rifles. This is known as the "Oropesa" technique.

Minesweepers also had an electrical system used to reduce their magnetic field, in order to avoid detonating magnetic mines. Other devices were used to create a field strong enough to detonate mines at a distance. Against acoustic mines, minesweepers used a sound-making machine made of a hammer hitting on a case.

Hope the above helps.

Nick Clark
www.harry-tates.org.uk