. . is likely to be useful at 2000 mph. It is correct that the YF12A was never deployed, because forces in the Pentagon were dead set against it because it would negate a Soviet threat they were shrilly promoting.
Since there were no other planes that could intercept modern bombers like the Backfire, "intelligence" and the Pentagon were either lying about the Soviet threat, or they were perfectly willing to compromise national security for political gain - your choice.