Minesweepers

A minesweeper is a small naval warship designed to engage in minesweeping. Using various mechanisms intended to counter the threat posed by naval mines, waterways are maintained clear for safe shipping.

Although naval warfare has a long history, the earliest known usage of the naval mine dates to the Ming dynasty. Dedicated minesweepers, however, only appear in the historical record several centuries later, to the Crimean War, where they were deployed by the British. In the Crimean War, minesweepers consisted of British rowboats trailing grapnels to snag the mines. Despite the use of mines in the American Civil War, there are no records of effective minesweeping being used. Officials in the Union Army attempted to create the first minesweeper but were plagued by flawed designs and abandoned the project. Minesweeping technology picked up in the Russo-Japanese War, using aging torpedo boats as minesweepers.

In Britain, naval leaders recognized before the outbreak of World War I that the development of sea mines was a threat to the nation's shipping and began efforts to counter the threat. Sir Arthur Wilson noted the real threat of the time was blockade aided by mines and not invasion. The function of the fishing fleet's trawlers with their trawl gear was recognized as having a natural connection with mine clearance and, among other things, trawlers were used to keep the English Channel clear of mines. A Trawler Section of the Royal Navy Reserve became the predecessor of the mine sweeping forces with specially designed ships and equipment to follow. These reserve Trawler Section fishermen and their trawlers were activated, supplied with mine gear, rifles, uniforms and pay as the first minesweepers. The dedicated, purpose-built minesweeper first appeared during World War I with the Flower-class minesweeping sloop. By the end of the War, naval mine technology had grown beyond the ability of minesweepers to detect and remove.

...
Wikipedia