In 1941, writes Stephen Budiansky in his wonderful new book, Blackett’s War: The Men Who Defeated the Nazi U-Boats and Brought Science to the Art of Warfare, “after a year of unbroken and devastating U-boat onslaughts, the British War Cabinet decided to try a new strategy in the foundering naval campaign. To do so, they hired an intensely private, bohemian physicist who was also an ardent socialist.”
Some of Britain’s best minds were already working on the Enigma project, attempting to decipher Germany’s coded radio messages. So Blackett put together an unusual team of “leftover” scientists: chemists, astronomers, actuaries, and biologists—including one who specialized in the sex life of the oyster. And for the next year, they put aside their own research and devoted themselves to solving the U-boat problem. According to Budiansky:
In April 1941, a month after starting work at Coastal Command, paid a visit to the operations room of Western Approaches Command in Liverpool, where a large wall map displayed the current estimated positions of all U-boats in the Atlantic. Blackett knew the number of hours being flown by Coastal Command aircraft and the areas they were patrolling. “I calculated in a few lines of arithmetic on the back of an envelope the number of U-boats which should have been sighted by the aircraft,” given the actual number of U-boats operating in the area as shown on the wall of the Western Approaches Command. The theoretical number Blackett obtained from his quick calculation was four times the actual number of sightings that Coastal Command air patrols were reporting. “This discrepancy,” Blackett continued, “could be explained either by assuming the U-boats cruised submerged or by assuming that they cruised on the surface and in about four cases out of five saw the aircraft and dived before being seen by the aircraft. Since U-boat prisoners asserted that U-boats seldom submerged except when aircraft were sighted, the second explanation was probably correct.” All of the obvious solutions were recommended: equipping the aircrews with better binoculars, avoiding flying into the sun, improving training. Then, discussing the problem one day, an RAF wing commander asked Blackett, “What color are Coastal aircraft?”
They were in fact mainly black, as they were mostly night bombers diverted from Bomber Command. Night bombers were painted black to reflect as little light as possible from searchlights. But by day, under most conditions of cloud and sun, an aircraft is seen as a dark object against a light sky. Tests were quickly ordered and it was verified that repainting the aircraft white reduced by a fifth the average maximum distance at which the planes could be seen. The undersurfaces of the wings were the part of the aircraft that stood out in particular contrast to the sky, and a scheme of using glossy reflective white paint for these surfaces was adopted. Williams calculated that the change to white camouflage would increase the number of U-boat sightings, and sinkings, by 30 percent. The plan was implemented within a few months. Air patrols during the winter had been yielding one U-boat sighting per every 700 hours of flying. By summer 1941, with the camouflage change and other improvements, the yield had doubled to one sighting per 350 hours.