a curving approach path. The NDRC estimated that lights could be spaced up to about apart without becoming visible as individual objects at a distance of . On this basis, it calculated that a large aircraft like a B-24 Liberator bomber could be camouflaged against the sky for a power consumption of under 500 watts. The key technology investigated under Yehudi was therefore the use of forward-facing lights to anti-submarine and attack aircraft. Ground prototyping To improve confidence in the approach, the project made a prototype in the form of a counter-illuminated plywood silhouette of a Liberator at life size, suspended from towers at a point where it could be seen from a point a little above sea level away across Oyster Bay, Long Island, so that it was seen mainly over water as a sea search aircraft would be from a submarine's conning tower. It was fitted with sealed beam lamps made by General Electric. The lamps had reflectors to give them a narrow beam of 3 degrees horizontally, 6 degrees vertically, to minimise power consumption for the required brightness. The lamps' brightness was controllable with a variable resistor. During a test in the winter of 1943, selecting a day when the visibility was above and the wind not so strong as to destroy the prototype, the observers could clearly see the thick cables used to hold up the model, but the silhouette itself was "completely invisible" with the lamps correctly adjusted. Aircraft trials The Yehudi project therefore used forward-pointing lamps mounted in the aircraft's nose and the leading edges of the wings, or suspended beneath the wings, their brightness controlled by a circuit containing a pair of photocells to match the brightness of the sky. One photocell pointed at the sky, the other at an auxiliary lamp; the circuit adjusted lamp brightness to make the output from the two photocells equal. It was trialled in Liberators, Avenger torpedo bombers and a Navy glide bomb from 1943 to 1945. By directing the light forwards towards an observer (rather than towards the aircraft's skin), the system provided effective and efficient counter-illumination camouflage, more like that of marine animals such as the firefly squid than the Canadian diffused lighting approach. The system never entered active service. Results In 1945 a Grumman Avenger with Yehudi lights got within of a ship before being sighted, when under the same conditions an uncamouflaged plane