Mines complemented U-boats, surface gunfire, torpedoes, and Luftwaffe bombing in Germany's effort to disrupt shipping around Britain. The new magnetic weapon threatened ships in swept channels and close to harbor entrances, places where crews expected navigation to be controlled. HMS Vega was damaged off Harwich on 7 November 1939, and HMS Blanche was sunk in the Thames estuary six days later. HMS Gipsy struck a mine after leaving Harwich on 21 November. Within two weeks, the weapon had damaged or sunk three destroyers around Britain's own approaches.
Chapter · 25:33-27:02
Magnetic mines threaten Britain's destroyers
The new German magnetic mine quickly damaged or sank destroyers near swept channels and harbor approaches in the autumn of 1939.