Finnish soldiers advancing under barbed-wire obstacles on the Hanko front. Fearing an assault over the ice during the oncoming winter, the Soviet garrison fled during the night of 2 December 1941. The evacuation of Hanko itself was performed in several convoys, between October 16 and December 2, 1941, which managed to transport roughly 23,000 troops to Leningrad. The fleet suffered casualties from Finnish minefields and coastal artillery, losing 3 destroyers and 2 large transports (Andrei Zhdanov and Iosif Stalin) as well as several smaller vessels. Finnish troops entering the area found it heavily mined.
Book "Finland at War: The Continuation and Lapland Wars 1941-45" by Vesa Nenye, Peter Munter, Toni Wirtanen and Chris Birks