It was being talked about as part of the response to "Moonlight Sonata" in November 1940. The "
Cold Water" countermeasures envisaged “cats eye” Hurricanes patrolling the beacon at Fécamp (where returning bombers switched on their navigation lights) but this wasn't done in the event. Also mooted, then dropped, was the idea of sending Blenheim night fighters on intruder missions to bomber bases. It would have meant removing their A.I. sets to ensure none fell into German hands. Reinstalling the gear in the aircraft would have kept at least one squadron out of action “possibly for a number of days ... which was not considered worthwhile.”