The work was compartmented — different engineers knew different parts of the system, and nobody knew more than they needed to know to do their specific job.

The results were aircraft that could not be built by conventional means and missions that could not be officially acknowledged.

The U-2 reconnaissance aircraft, which Lockheed developed in extraordinary secrecy through the mid-1950s, could fly above 70,000 feet — higher than any Soviet fighter could reach.

It was used to photograph Soviet military installations, nuclear facilities, and whatever else the CIA and the Air Force wanted to see from altitudes that seemed safe from interception.

The program was so secret that when a U-2 was shot down over the Soviet Union in 1960, the initial American cover story was that it was a weather aircraft that had gone off course.