Oxcart was one of its kind, a sophisticated aircraft designed during the Cold-War era. Its body was made up of titanium. Titanium was only found in substantial quantities in the then Soviet Union. The USA brought huge amounts of titanium from the Soviets (as told in Net Geo's documentary: Inside: Area 51's secret)
Now, how did the USA get the titanium from the Soviets? Didn't the Soviets know about it? If it knew, why were no actions implemented?