F-111 Aardvark
The reason why all of these planes are built for speed is simple. Stealth. During war time you cannot afford to be noticed by the enemy, and to hit first, these planes were developed and used for specific air raids and gathering intel.
The Aardvark is a two person plane which started its service with the US Air Force in 1967. Though it was in action for more than 30 years, the US decided to discontinue the line in 1998. Maybe because it costs $25 million dollars per unit?