This declassified cover image from a 1956 document titled "Project 1794, Final Development Summary Report" shows an artist's concept of U.S. Air Force plans for a flying saucer. Built by Canada's Avro Aircraft, the saucer was supposed to fly at speeds of up to Mach 4. But apparently, it barely got off the ground.
Avro had built the controversial Arrow supersonic interceptor, which was abruptly cancelled in 1959. Project 1794, the plan to build a flying saucer for the U.S. Air Force, never got beyond the testing phase.