The Lockheed U-2 spy plane operated by the CIA over Soviet airspace from 1956 until Gary Powers was shot down in '60 (and thereafter over less well defended airspace) used flight at modest speed but exceptionally high altitude to evade air defenses, but it was clear from the start that surface to air missiles would soon win the altitude race and start knocking them down. In 1956 the CIA started shopping for a reconnaissance aircraft that could survive over the USSR using great speed and a reduced radar cross section (a beta version of stealth), a contest ultimately won by the Lockheed A-12 in '59. The SR-71 for USAF was a development of the A-12 that added more equipment and a second seat, and the A-12 was retired in '68. These were very cool aircraft.
But building those meant that we wouldn't be building some very cool Convair proposals. Convair was already building the B-58 Hustler for USAF:
...and their first crack at the CIA contract was a proposal for a complex three vehicle manned/unmanned parasite aircraft based on the proposed bigger and meaner USAF B-58B Super Hustler, which ends up looking like some kind of large insectoid alien space fighter:
Yo, I heard you liked spikes... other proposals managed to dial back the spikes slightly by adding a Concorde-ish articulating nose for landing a single hulled manned parasite:
The Super Hustler would carry both to a high speed and altitude where the parasites would drop as a single unit and the ramjets fire. The unmanned parasite would help push the manned parasite to ludicrous speed until it was near the target, where the unmanned parasite would detach, dive away and nuke the everlovin' shit out of whatever the manned parasite was about to photograph (Convair had a real hardon for nuking the Soviets and a firm belief in "reconnaissance in force"). But the CIA seemed insistent on strictly limiting nuclear war, so, reluctantly, the unmanned parasite could swap out the bomb for fuel and be jettisoned when empty to impact with rather less effect.
Fuck you, simplicity. Alas, Convair was having enough trouble with the regular ol' Hustler, which was delivered way over budget and was a maintenance nightmare, and the CIA gently dissuaded them from continuing with developing anything remotely like this, ever. So they went back to the drawing board and came back with the somewhat simplified and badass looking FISH, or First Invisible Super Hustler, a single parasite aircraft of supposedly better projected performance than the A-12 with a substantially lower radar cross section compared to the early A12 designs (which lacked some of the final stealthy features):
Then USAF cancelled the B-58B.
Fine, Convair said, how about a standalone, equally cool looking aircraft called the Kingfish?:
Look at it. Damn dude, this was 1959! That is a mean, advanced looking aircraft. An interesting brute force wedge-o'-thrust contrast to the long and sinuous A-12/SR-71.
Anyway, the final A-12 proposal closed the difference in radar cross section with the Kingfish and Convair lost to Lockheed on the basis of range, max altitude, and cost - and you might suppose that Convair had burned a fair amount of credibility by frequently ignoring the KISS principle. However, at about this same time Convair was applying themselves to ICBM and manned space rockets, developing the highly successful Atlas family and others. Perhaps the wickedly complex world of multi-stage rocket design led them astray early in the competition.