Commissioned at Vancouver April 2, 1942, HMCS Caraquet was built for the Royal Navy and transferred to the RCN. Caraquet served on the West Coast from May 1942 to March 1943, on the East Coast from May 1943 to February 1944 and on the English Channel for invasion duties. National Archives of Canada, PA-125863.

Since WWI, Germany's warships and submarines had enough autonomy to lay mines along both the American and European Atlantic shores. In 1939, when war became imminent, the Allies feared they might face extensive minefields blocking their harbours and threatening sea routes. At that time, the Royal Canadian Navy (RCN) had only four minesweepers: HMCS Comox, Fundy, Gaspe and Nootka. The situation was an emergency and called for a rapid response.

The Canadian Government authorized the construction of Bangor class minesweepers. Like corvettes, these were ships with a light draught, that did not require the same degree of shipbuilding expertise as cruisers and destroyers did. They could be built in inland shipyards, along the St. Lawrence and the Great Lakes.

The RCN will have up to 54 Bangor class minesweepers; since the threat from German mines never reached the expected level, many were used to escort convoys along the Atlantic coasts and in the Gulf of St. Lawrence. Later on, German mines will be a threat along the coats of Normandy in June 1944, and Canadian minesweepers will work together with the Royal Navy to clear the Channel.

Diagram:Minesweeping

Canadian shipyards also built an improved version of Bangor class vessels, known as the Algerine class. There were 41 such ships built in Canada, mostly at the Port Arthur shipyards. Of that number, only 12 served in the RCN; they were used as escort ships, and did not carry minesweeping gear.

Minesweeping Techniques

German contact mine in waters off Nova Scotia, 2 June 1943.   Photo by H.H. Black. Department of National Defence / National Archives of Canada, PA-178962.

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 have 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.