By 1940 the Royal Navy had realized that the Bangor-class minesweepers were too small to carry the equipment needed to handle magnetic mines.

[citation needed] A bigger ship was designed, ironically about the same size as the older Halcyon class that the Royal Navy had rejected earlier as too large and expensive for mass production.

The turbine group had a draught of 11 feet (3.4 m) while the reciprocating engined ships sat 1 foot 3 inches (0.4 m) deeper in the water.

The engines produced a total of 2,000 shaft horsepower (1,500 kW) and gave a maximum speed of 16.5 knots (30.6 km/h; 19.0 mph).

They carried a maximum of 660 long tons (671 t) of fuel oil that gave them a range of 5,000 nautical miles (9,300 km; 5,800 mi) at 10 knots (19 km/h; 12 mph).

Many Canadian ships omitted their sweeping gear in exchange for a 24-bomb Hedgehog spigot mortar and a stowage capacity for 90+ depth charges.

A total of 94 Algerine class vessels served with the Royal Navy; of these 45 were built in the UK and another 49 in Canada.

[3] Of the ships built in Canada, the companies involved were Toronto Shipbuilding (later Redfern), Port Arthur and Collingwood.

Fourteen ships were built for the United States Navy, but again were transferred to the RN on completion under Lend-Lease.

Of the RN ships, five were transferred to the Belgian Navy, two to South Africa and two to Ceylon; another five, one apiece, were acquired by Burma, Nigeria, Italy, Iran, and Thailand.