Oropesa sweep

Oropesa sweep, a method of sweeping moored mines by a wire towed by a single minesweeper. It swept mines to the side of the minesweeper by means of a long wire fitted with wirecutters placed at intervals along the wire to cut the mines' moorings. The wire was towed astern of the minesweeper with a kite fitted to the wire a short distance from the point of tow to keep the wire down to a fixed depth below water. Near the end of the wire was an otter which forced it outwards as it was towed through the water, and at the end was a float to hold the wire at its fixed depth and prevent it sinking to the bottom. As the wire came into contact with the mines' mooring wires, they slid along it until meeting a cutter. This severed the mooring wire so that the mine floated to the surface where it was destroyed by rifle fire.

This form of sweep was first developed in 1919 in the minesweeper Oropesa during the clearance of the northern mine barrage laid during the First World War (1914–18). This ran across the North Sea from the Orkney Islands to the Norwegian coast. It was improved between the two world wars by the substitution of multi-plane otters for the earlier single otter used for spreading the sweep, and by better designs of cutters.