I also have an encyclopedia from 1982 that states that part of the break in the 'century series' numbering was to go on a stealth aircraft.
I read that one way of knowing these aircraft existed was looking at the defence spending, there was a black hole that was unaccounted for.
Saw something on area 51 that claimed it was the test centre for the U2 and SR-71. Amazingly the staff carried around a chart that had times of the day printed on it, the times were when Soviet spy satellites were due overhead. As the times approached, everything would get towed indoors and once the satellites passed over the aircraft would get towed out again. But what gave the secrets away was when the aircraft were outside their shadow would cause a difference in temperature on the concrete apron that would leave an outline that would show up on a IR camera. So some American with a sense of humour played tricks by drawing fake outlines of funky shaped aircraft with pots of paint. It was a good trick as it fooled the Soviets into thinking the US had superior technology.
