On 15 September 1940, three weeks after commissioning, Bismarck left Hamburg to begin sea trials in Kiel Bay.[17] Sperrbrecher 13 escorted the ship to Arcona on 28 September, and then on to Gotenhafen for trials in the Gulf of Danzig.[18] The ship's power-plant was given a thorough workout; Bismarck made measured-mile and high speed runs. As the ship's stability and manoeuvrability were being tested, a flaw in her design was discovered.