This is only true because before the array of satellites deployed by the US military, there was no other system for finding your global position.
Not true. From the Wikipedia entry on the SR-71"Nortronics, Northrop's electronics development division, had developed an astro-inertial navigation system (ANS), which could correct navigation errors with celestial observations, for the SM-62 Snark missile, and a separate system for the ill-fated AGM-48 Skybolt missile, the latter of which was adapted for the SR-71.[50][citation needed]
Before each takeoff, a primary alignment brought the ANS's inertial components to a high degree of accuracy. Once in flight, the ANS, which sat behind the Reconnaissance Systems Officer (RSO)'s position, tracked stars through a circular window of quartz glass set in the upper fuselage.[37] Its "blue light" source star tracker, which could see stars during both day and night, would continuously track a variety of stars as the aircraft's changing position brought them into view. The system's digital computer ephemeris contained data on 56 (later 61) stars.[51] The ANS could supply altitude and position to flight controls and other systems, including the Mission Data Recorder, Auto-Nav steering to preset destination points, automatic pointing and control of cameras and sensors, and optical or SLR sighting of fix points loaded into the ANS before takeoff.[52] Former pilot Richard Graham told an interviewer at the Frontiers of Flight Museum that the navigation system was good enough to limit drift to 1,000 feet off the direction of travel at Mach 3."
I knew a guy who worked on this system. He told me about a time when they pulled one out of a plane for routine maintenance and they thought it was malfunctioning as it locked onto a star while in the hanger. After they couldn't find the fault they put a guy on a lift and turned all of the lights off in the hanger. Sure enough they found a pin hole in the roof that could only be seen close up in the dark. After they patched the hole, everything checked out fine.