During the first two years of the Korean War, all US Naval ship losses and 70 percent of our casualties were directly related to mine warfare. Minesweeping personnel made up only 2 percent of our naval forces in Korea, but accounted for over 20 percent of our naval casualties.

A minefield is a strategic, rather than tactical, weapon. A field is generally seeded with a variety of devices. The most primitive explode on contact or detonate magnetically when they pick up the magnetic field of a passing ship.

Clearing lanes required the sweepers to sail in straight lines, which made them extremely vulnerable to fire from shore batteries such as those on Sin-Do.

The 3,000 mines used at Wonsan were moored, magnetic types, together with simple contact mines comprising the least sophisticated naval mines used during WWII, but their fields were well planned by Russian advisers.

The method of clearing these fields was to use minesweepers towing paravanes, a torpedo-shaped float similar in shape to a Harvey Torpedo, which is pulled away from the ship towing it, moored mines being snagged and deflected away from the ship towards the paravane by the towing wire, where it is exploded, or sunk, by cannon fire.

There are several types of minesweeping procedures. In this image, mechanical Sweeps are designed to sever the cables of moored mines. A sweep wire is towed by the minesweeper so as to snag the tether cables of mines and sever them through abrasive action or with explosive cutters located along the sweep wire. Severed mines float to the surface and may be dispatched by gunfire or UDT directly.