A type M9B Norden Bomb Sight from WWII. One of the most precious gear of the US Army. In great condition, untested.

The Norden Mk. XV, known as the Norden M series in U.S. Army service, is a bombsight that was used by the United States Army Air Forces (USAAF) and the United States Navy during World War II, and the United States Air Force in the Korean and the Vietnam Wars. It was an early tachometric design, which combined optics, a mechanical computer, and an autopilot for the first time to not merely identify a target but fly the airplane to it. The bombsight directly measured the aircraft's ground speed and direction, which older types could only estimate with lengthy manual procedures. The Norden further improved on older designs by using an analog computer that continuously recalculated the bomb's impact point based on changing flight conditions, and an autopilot that reacted quickly and accurately to changes in the wind or other effects.

Together, these features promised unprecedented accuracy for daytime bombing from high altitudes. During prewar testing the Norden demonstrated a 150 feet (46 m) circular error probable (CEP)[a], an astonishing performance for that period. This precision would enable direct attacks on ships, factories, and other point targets. Both the Navy and the USAAF saw it as a means to conduct successful high-altitude bombing. For example, an invasion fleet could be destroyed long before it could reach U.S. shores.

To protect these advantages, the Norden was granted the utmost secrecy well into the war, and was part of a production effort on a similar scale to the Manhattan Project: the overall cost (both R&D and production) was $1.1 billion, as much as 2/3 of the latter or over a quarter of the production cost of all B-17 bombers. The Norden was not as secret as believed; both the British SABS and German Lotfernrohr 7 worked on similar principles, and details of the Norden had been passed to Germany even before the war started. Courtesy of Wikipedia