hypersonic

http://www.dailymail.co.uk/sciencetech/article-2855802/Is-proof-mysterious-bangs-heard-sides-Atlantic-caused-secret-jet-Footage-hypersonic-engine-action-reveals-sounds-identical-unexplained-noises.html

http://www.dailymail.co.uk/sciencetech/article-2855795/So-secret-existence-not-acknowledged-Futuristic-Aurora-spy-plane-travels-SIX-TIMES-speed-sound-blamed-mysterious-booms-heard-weekend.html