My understanding is that Kelly Johnson and his team went from paper to flying in 18 months. I got to see one of these refueled from a tanker plane. We were on the Iowa-IL state line when the Bird called in, telling us he was slowing down for link-up...he just passed Billings, Montana!
That is what Brian Shul says, as well. He noted that after Lt. Powers had been shot down in the U2, President Eisenhower said to give him an aircraft they could NOT shoot down. Eighteen months later, they had the SR-71.
Some excellent comments and stories
in this YouTube video of Shul making a presentation. It's nearly an hour long, but by the time I got to the end, it seemed as if only 10-15 minutes had gone by.