"Kormoran" departed German waters during December 1940, under the command of "Fregattenkapitän" (Commander) Theodor Detmers. After operating in the Atlantic, during which time she sank seven merchant ships and captured an eighth, the raider sailed to the Indian Ocean in late April 1941. Only three merchantmen were intercepted during the next six months, and "Kormoran" was diverted several times to refuel German support ships. As the raider was carrying several hundred sea mines and was expected to deploy some of these before returning home in early 1942, Detmers planned to mine shipping routes near Cape Leeuwin and Fremantle, but postponed this after detecting wireless signals from a warship (Australian heavy cruiser ) in the area. Instead, he decided to sail north and investigate Shark Bay. At the time of the battle, the raider was disguised as the Dutch merchantman "Straat Malakka", and carried 399 personnel: 36 officers, 359 sailors, and 4 Chinese sailors hired from the crew of a captured merchantman to run the ship's laundry.