Widder (HSK 3) was an auxiliary cruiser (hilfskreuzer) of the German Navy that was used as a merchant raider in the Second World War. Known to the KM as Schiff 21, to the Royal Navy she was Raider D. The name Widder (Ram) represents the constellation Aries in the German language. The name was given after the horoscope sign of the ship's master, Kapitan zur See Helmuth von Ruckteschell.
Built for HAPAG, the Hamburg America Line, at Howaldtswerke, Kiel, she was launched in 1930 as the freighter Neumark. After an uneventful career she was requisitioned by the Kriegsmarine for use as a commerce raider. She was converted for this purpose by Blohm and Voss in the winter of 1939, and commissioned as the raider Widder on 9 December of that year. She sailed on her first and only raiding voyage in May 1940.
Deemed unsuitable as a merchant raider, Widder was re-christened Neumark, and used as a repair ship in Norway. After the war she was taken into British service as Ulysses, then sold back to Germany as Fechenheim in 1950 before being wrecked off Bergen in 1955.
She was one of only two German auxiliary cruisers to survive the war, after one 1940 cruise. Her captain, Kapitän zur See Helmuth von Ruckteschell, was one of only two German naval commanders convicted of war crimes at the end of the war.