Operation Fernbank

'Fernbank' was a British naval undertaking to create and disseminate false information about Allied anti-submarine weapons and their capabilities (September 1943/1944).

The object of this deception undertaking was to persuade the Germans to keep their U-boats within the current depth capability of the British depth charges. The 'story' promulgated by this deception was that the British had developed the MFR rocket-propelled depth charge which was more powerful, longer ranged and capable of working at greater depths than current depth charges, but which could not be used at depths of less than 300 ft (90 m) as the detonation was so destructive that it would damage the attacking warship.