'Balderdash' was a British unrealised deception plan to lure a substantial portion of the German navy’s surface strength into a major battle (April/May 1942).

The plan, which was cancelled before implementation, was based on the use of the radio transmitter of a captured German intelligence vessel to transmit to German fleet headquarters a false message, whose apparent veracity was to be supplemented by a report from a double agent in Iceland, that the British Home Fleet had departed British waters for Iceland, leaving British water open to a major German naval raid.