During the summer, the extension of the convoy system and effectiveness of the escorts made the east coast of Britain as dangerous for the U-boats as the Channel had become. In this period, the Flanders flotilla lost a third of its boats, and in the autumn, losses were at 40%. In October, with the German army in full retreat, the Flanders flotilla was forced to abandon its base at Bruges before it was overrun. A number of boats were scuttled there, while the remainder, just ten boats, returned to bases in Germany.