The Boeing Model 853-21 Quiet Bird was a US Army reconnaissance plane study developed by Boeing in the early 1960s from their Model 831. It was an early example of stealth technology, especially electromagnetic low-observability.
Development of the Model 853-21 began in 1962 at Boeing Wichita, only a 1/2 scale prototype was produced which never flew, but tests showed that it had a very low radar cross-section (stealth aircraft).