The Flower class comprised five sub-classes of sloops built under the Emergency War Programme for the Royal Navy during World War I, all of which were named after various flowers. They were popularly known as the "herbaceous borders," in humorous reference to a well-known adage about the Royal Navy ("Britain's best bulwarks are her wooden walls"), as well as to a type of garden border popular in the United Kingdom.
The "Flowers" were designed to be built at merchant shipyards, to ease the pressure on yards specializing in warships. The initial three groups were the first purpose-built fleet minesweepers, built with triple hulls at the bow to give extra protection against loss from mine damage when working. When submarine attacks on British merchant ships became a serious menace after 1916, the existing Flower-class minesweepers were transferred to convoy escort duty, and fitted with depth charges, as well as 4.7-inch naval guns.
The Gentian and the Myrle were both lost to mines in the Baltic on 2 July 1919.
The latter two groups, the Aubretias and Anchusas, were designed as submarine decoys, or Q-ships, with hidden guns and a distinctive "merchant marine" appearance. These "warship-Qs" were thus the first purpose-built anti-submarine fighting ships, and their successor types were the anti-submarine sloops of World War II , which evolved into the modern anti-submarine warfare frigate during the 1939-45 Battle of the Atlantic.
Some 112 "Flowers" in total were built for the Royal Navy, and a further eight for the French Marine Militaire. Of these, 17 British and one French "Flowers" were sunk.