 By the time the aircraft was close enough to the U-boat's position to illuminate with the Leigh light, the U-boat was well under the water.As a bonus, the Metox set would also provide warning in excess of visual range in daylight.In December 1942 British codebreakers regained the ability to decipher messages encrypted with naval Enigma machines and the Germans noticed the resulting increase in U-Boat sightings.