The Wild Cat Scheme was a system during WWII - used by the brits to make the Germans send messages in code on quiet days.

To be able to break codes encrypted with the Enigma, the brits would have to have something to work on.

Using the Wild Cat Scheme basically meant that a small vessel would start sending random letters in Morse, using german morse equipment and frequencies.

A german vessel receiving this, presuming the british vessel transmitting Enigma code, but would (obviously) not be able to decode the message. The german vessel would then transmit something along the lines of "What the hell are you trying to say - learn how to use your cipher machine".

The brits would then use this encoded message on their bombe to try and find the current day's settings. Very cunning :)

Enigma