...there's always been speculation among enthusiasts about how fast the SR-71 Blackbird (center of picture) really could fly. ...during the Cold War, every time the Soviet Union attempted to set a new world speed record with one of their latest jet planes, the US Air Force would roll out an SR-71 and break the record just set by the USSR. ...the US Air Force only admitted to a speed in excess of Mach 3.0 (2283 mph)(3674 km/h) .................................................. So here's the definitive answer for those of you who want to add a little more trivia to your already full minds;-) The fastest published speed of the SR is Mach 3.5. There are several factors that limit the speed of the SR, one is the shock waves generated by various parts of the plane, at around Mach 3.6- 3.8 the shock wave off the nose of the aircraft narrows enough to go into the engine, while there is the inlet spike (which slows the air to subsonic before it enters the engine), the shock wave bypasses the spike and causes the engine to unstart. Second is the heat generated by the plane moving through the atmosphere, even titanium has it's limits, and the heat generated by the SR brings the fuselage to the brink. Just recently I found out that during a Lockheed Skunk Works study to see how much money and development it would take to get the SR to go faster than it's designed top speed 3.2- 3.5, the designers discovered (among other things) that the metal divider between the windshield was heating up so much above mach 3.5 that it was affecting the integrity of the windshield, and at that point they had stretched the glass technology to the max! So Mach 3.2 to a max of 3.5. Now according to Richard Graham: "The design Mach number of the SR-71 is 3.2 Mach. When authorized by the Commander, speeds up to Mach 3.3 may be flown if the CIT limit of 427 degrees C. is not exceeded. I have heard of crews reaching 3.5 Mach inadvertently, but that is the absolute maximum I am aware of." (Graham obviously making his remarks during the time the SR-71 was in use). Bill P.S. The SR-71 flew operationally from 1964 to 1998. The picture above is in the main gallery of the Boeing Museum of Flight in Seattle, Washington. "What I Saw"