By 1940 the Royal Navy had realized that the s were too small to carry the equipment needed to handle magnetic mines. A bigger ship was designed, ironically about the same size as the older that the Royal Navy had rejected earlier as too large and expensive for mass production. The size of the new ship made them suitable for use as ocean-going escort ships and many were used in that role to fill a critical shortage of escorts. In fact most of the ships built for the RCN were solely employed as such and were fitted with more dedicated anti-submarine weapons than the RN ships. To maximise production, alternate designs were made to use either steam turbines or reciprocating steam engines. The construction contracts were awarded to shipbuilders in both the United Kingdom and Canada.
The turbine-powered ships displaced at standard load and at deep load while the reciprocating group displaced at standard load and at deep load. The hull's dimensions were the same for both groups and the ship measured long overall with a beam of. The turbine group had a draught of while the reciprocating ships sat deeper in the water. The ships' complement consisted of 85 officers and ratings. The turbine-powered ships had two Parsons geared steam turbines, each driving one shaft, using steam provided by two Admiralty three-drum boilers. The engines produced a total of and gave a maximum speed of. The reciprocating ships had two vertical triple-expansion steam engines totalling and reached the same speed. They carried a maximum of of fuel oil that gave them a range of at. The Algerine class was armed with a QF Mk Vanti-aircraft gun and four twin-gun mounts for Oerlikon 20 mm cannon. The latter guns were in short supply when the first ships were being completed and they often got a proportion of single mounts. By 1944, single-barrel Bofors 40 mm mounts began replacing the twin 20 mm mounts on a one for one basis. All of the ships were fitted for four throwers and two rails for depth charges. Many Canadian ships omitted their sweeping gear in exchange for a 24-barrel Hedgehogspigot mortar and a stowage capacity for 90+ depth charges.
Ships
Post-war service
After the war, a number continued in service as patrol boats, survey ships, and training ships. On 11 March 1959 HMS Acute and HMS Jewel, training ships at Dartmouth, rescued the burning German coaster Vorman Rass, off Start Point, Devon. Some were sold to other navies or into merchant service. At least one, HMS Pickle was still engaged in minesweeping duties in British waters as late as 1955. At least one Algerine is still in service with the Royal Thai Navy: HTMS Phosampton.
