 Complete the following phrase:  Most of the heavy ships of the Kriegsmarine were used as commerce raiders in the early years of the war. Two of the panzerschiffe, Deutschland and Graf Spee, were already at sea at the outbreak of war; the former found little success and the latter was ultimately trapped and forced to scuttle after the Battle of the River Plate in December 1939. From October 1940 to March 1941, Admiral Scheer went on her own raiding operation and captured or sank seventeen ships, which made her the most successful of the German capital ship surface raiders in the entire war. Scharnhorst and Gneisenau conducted Operation Berlin, a major sortie into the Atlantic in early 1941. Bismarck and Prinz Eugen went on the last Atlantic raiding mission, Operation Rheinübung, in May 1941. Bismarck sank the British battlecruiser but was herself sunk three days later. The loss of Bismarck led Hitler to prohibit further sorties into the Atlantic; the remaining capital ships were concentrated in Norway for use as a fleet in being and to threaten convoys to the Soviet Union on the 