Considering Lockheed's SR-71 "Blackbird", a strategic Mach 3+ reconnaissance aircraft, first flew in 1964, we can only imagine what kind of top-secret aircraft the military is currently using. However, before the SR-71, there was Project 1794, "an all-powerful fully-functioning flying saucer to patrol the skies; in a 1956 memo it is acknowledged that the craft was to reach top speeds of 'between Mach 3 and Mach 4, a ceiling of over 100,000 ft. and a maximum range with allowances of about 1,000 nautical miles'." Continue reading for a video and more information.
Engineers working on the project got so far as initial rounds of product development and had begun prototype design before their endeavors crashed. Had they been successful, a stratosphere-spinning saucer would have been unleashed, boasting speeds of up to 2,600 miles per hour and the ability to take off and land vertically, controlled and stabilised by propulsion jets. That would have meant a trip from New York to Miami would have taken a mere 24 minutes.