How about the B-36? The largest combat aircraft of all time, obsolete from the get-go, took 12 years to develop and was phased out two years after entering service, enormous cost overruns resulting in SecDef cancelling the contract on an aircraft carrier to fund it...
Oh, and it never flew a single combat mission.
Set the standard for incredibly expensive, theoretically awesome, but utterly useless planes from the XB-70 to the A-12 the the F(not A)-22.
Say it ain’t so! Jimmy Stewart made a movie years ago; he was playing the part of a pilot flying these planes in an AF command some place.
Steve