In the 1830s the term was adopted by the RN for sailing warships of roughly similar size, primarily operating in the shipping protection role.

The months leading up to World War II saw the RN return to the concept of a small escort warship being used in the shipping protection role.

The Flower class was based on the design of Southern Pride, a whale-catcher, and were labelled "corvettes", thus restoring the title for the RN, although the Flower-class has no connection with pre-1877 cruising vessels.

In early 1939, with the risk of war with Nazi Germany increasing, it was clear to the Royal Navy that it needed more escort ships to counter the threat from Kriegsmarine U-boats.

To meet this requirement, the Smiths Dock Company of South Bank -on-Tees, a specialist in the design and build of fishing vessels, offered a development of its 700-ton, 16 knots (18 mph; 30 km/h) whaler (whale catcher) Southern Pride.

The Flower class became an essential resource for North Atlantic convoy protection until larger vessels such as destroyer escorts and frigates could be produced in sufficient quantities.

The simple design of the Flower class using parts and techniques (scantlings) common to merchant shipping meant they could be constructed in small commercial shipyards all over the United Kingdom and Canada, where larger (or more sophisticated) warships[8] could not be built.

Apart from providing a very useful space where the whole crew could gather out of the weather, the added weight improved the ships' stability and speed and was applied to a number of the original Flower-class vessels during the mid and latter years of the war.

The original Flowers had a mast located immediately forward the bridge, a notable exception to naval practice at that time.

The RN ordered fifteen modified Flowers from Canadian shipyards under the 1941 programme; eight of these were transferred to the USN under reverse Lend-Lease.

Due to shortages, a pair of Lewis guns or quadruple Vickers HMG was sometimes substituted for the pom-pom, which would have left the ship very vulnerable to aircraft attack in its envisaged role of coastal convoy escort and patrol in the North Sea.

Subsequent inventions such as the High Frequency Radio Direction Finder (Huff-Duff) were later added, along with various radar systems (such as the Type 271), which proved particularly effective in low-visibility conditions in the North Atlantic.

The Flower class had been designed for inshore patrol and harbour anti-submarine defence and many required minor modifications when the Allied navies began to use them as trans-Atlantic convoy escorts.

These small warships could be supported by any small dockyard or naval station, so many ships came to have a variety of weapons systems and design modifications depending upon when and where they were refitted; there is really no such thing as a 'standard Flower-class corvette' Several of the major changes that vessels in the class underwent are indicated below, in a typical chronological order: A ship could have any mix of these, or other specialist one-off modifications.

A good example of this is the difficulty that RCN Flowers had in intercepting U-boats with their Canadian-designed SW1C metric radar, while the RN vessels were equipped with the technologically advanced Type 271 centimetric sets.

[14] Men at action stations were drenched with spray and water entered living spaces through hatches opened for access to ammunition magazines.

[14] The head (or sanitary toilet) was drained by a straight pipe to the ocean; and a reverse flow of the icy North Atlantic would cleanse the backside of those using it during rough weather.

A typical action by a Flower encountering a surfaced U-boat during convoy escort duties was to run directly at the submarine, forcing it to dive and thus limiting its speed and manoeuvrability.

Continuous actions against a numerically superior U-boat pack demanded considerable seamanship skills from all concerned and were very wearing on the crews.

Construction of the Flower-class was superseded toward the end of the war as larger shipyards concentrated on River-class frigates and smaller yards on the improved Castle-class corvette design.

The Flower class represented fully half of all Allied convoy escort vessels in the North Atlantic during World War II.

The fledgling navy had intended to buy three more corvettes, as well as a number of surplus minesweepers, but severe budget restrictions cancelled these plans, leaving the original three to serve alone through the 1950s and 1960s despite antiquated armament, poor accommodation, and maintenance problems.

In November 1955, she rescued the freighter Makedonia in the North Pacific, towing the vessel for over one month through severe weather, becoming one of the most famous salvage ships of all time.

The surplus RCN Flowers Norsyd and Beauharnois were sold as mercantile freighters but were subsequently acquired in 1946 by the Mossad LeAliyah Bet, a branch of the Jewish Defense Association (Haganah) in the British Mandate for Palestine.

Allied navies disposed of their Flowers so quickly following the war, the RN could not supply a single vessel to play Compass Rose in the 1953 film production of Nicholas Monsarrat's novel The Cruel Sea.

She was laid up in reserve in March 1946 and converted in 1952 to a research vessel for Canadian Department of Marine and Fisheries, a role she served in until the early 1980s when she was acquired by the trust.