“During World War II the top secret “Norden XV” or “Blue Ox” otherwise known the Army Airforce’s “Norden M Series Bombsights,” were used up to and including the Vietnam War by all American military aircraft with bomb carrying capabilities. This bombsight was considered a “Canonical Tachometric Design” meaning that it had the ability to measure the aircraft's direction and ground speed. In time the Norden improved its original design by using a computer that constantly calculated the aircraft’s flight characteristic and external wind forces to determine the bomb's impact point. When the B-17 Flying Fortress was designed, it came equipped with a Sperry A-3 Autopilot that only corrected angular deviations in the aircraft’s straight and level course. In time most bombsights were replaced by video displays on the instrument panel. Dumb or gravity bombs were mostly replaced with in-flight guidance bombs, such as laser-guided bombs or those using a GPS system. The last combat use of the Norden bombsight was by the US Navy during the covert “Operation Igloo White” mission when OP-2E Neptune aircraft dropped electronic sensors to detect enemy activity along the Ho Chi Minh Trail. Project CHECO Southeast Asia Report was declassified on May 5, 2013.”