On 23 November 1945, Air Materiel Command (AMC) issued desired performance characteristics for a new strategic bomber "capable of carrying out the strategic mission without dependence upon advanced and intermediate bases controlled by other countries".Less than 10 years from concept to operational service!
First flying in December 1954, B-52B, AF Serial Number 52-8711, entered operational service with 93rd Heavy Bombardment Wing at Castle Air Force Base, California, on 29 June 1955.
[Wikipedia, B-52 Stratofortress]
... and: IT'S STILL FLYING!!!
This is the ideal for which the Pentagon ought to strive: from concept to operational service in 10 years, with useful life of 50+ years!