Cracking stuff. I remember sitting in the radio position in a Nimrod MR2 doing pre-flight stuff in Oman when the Omani AD network piped up on UHF Guard asking the aircraft at FL600 to identify themselves. No reply was heard so they challenged again and threatened to send their aircraft up to intercept the "intruder". I looked out of the window at the Omani Jaguars on QRA and thought "good luck with that". Wasn't sure if the high flyer was a U-2 or a SR-71, but checked the ATO and it confirmed that it was a U-2. Needless to say the Jaguars remained on the ground