Lockheed engineers used a titanium alloy to construct more than 90 percent of the SR-71, creating special tools and
manufacturing procedures to hand-build each of the 40 planes. Special heat-resistant fuel, oil, and hydraulic fluids
that would function at 85,000 feet and higher also had to be developed.
Initial orders for American sources of titanium were found not to be pure enough, so the US ordered titanium from the
USSR which was pure enough to make the alloy. Fortunately, the Russians never discovered that the titanium they sold
to the US during the Cold War was being used to build the SR-71s that would spy on them.
