The so called "Räumboote" - R-Boats were small minesweepers designs to operate in shallow waters like harbors, coastal areas or rivers. Between 1933 and the end of the war, about 300 of this boats were build in several series which did not differ very much.
Many of them had a quite special propulsion concept, no standard propellors and rudders, but horizontally mounted Voith-Schneider propellors which made the boats very maneuverable.
Besides their main operational task - mine sweeping - the R-Boats were used for several other duties, like convoy escorts, rescue missions or escorting U-boats in and out of their bases. They were used in all coastal areas under German command, especially in the British Channel and the Mediterranean.
Because of the light armament, a huge number of them were destroyed or damaged during wartime and about 140 survived the war. They were taken over by the allies, the USA got 48, the Soviet Union 45, Denmark 24, Britain 11, the Netherlands 8 and Norway got 4 of them. The R-Boats taken over by the Western Allies were used to form the "German Minesweeping Service" - "Deutscher Mienenräumdienst" to remove the minefields in european waters after the war.
24 were returned to Germany to form the mine sweeper squadrons of Bundesmarine in 1956 and used until the late 1960s.