How about this? It's recent, but retired from service. There was a moment when nobody was certain whether satellite surveillance would work or not, so somebody --either Ike or JFK-- approved buliding something that would fly so fast, so high, nothing could touch it:
Technically it wasn't originally developed for surveillance. It's a derivative of the super-secret YF-12. The air force *still* downplays the YF-12 in terms of capability, intent, and numbers made. Basically the YF-12 was a little shorter than the SR-71, and it carried 4 missiles. Each missile was air-to-air, and carried a small nuclear warhead. a non nuclear version of that missile became the AIM54 phoenix missile which the f-14's used.
The idea was, to have a mach 4-5 fighter jet that would fly at double the altitude any other aircraft could reach. I know they advertise the SR-71 as "mach3+", trust me that's a fair bit of understatement there. I mean when it lands, they have to wait for the plane's skin to cool off enough for the pilot to safely get out IN his well insulated spacesuit style flight suit. Bear in mind it gets that hot in freezing upper atmosphere, in very thin air, so high up you can see a star filled sky at noon. It goes so fast it takes hundreds of miles to make a U turn. The afterburners on the SR-71 and YF-12 are designed to be used continuously and are nearly as large as the turbofan engines they're hooked up to. At top speed it's basically an early "ramjet" engine.
The YF-12 had an enormous long range radar, and would fire nuclear tipped mach 5 air to air missiles at entire bomber squadrons, or shoot down ballistic missile warheads as they reentered the atmosphere from space (its radar dish could be pivoted upwards at a high angle... and there's no planes up there above it). It also had the range to go 'deep' into russia and clear out interceptors for US bombers. but it's main purpose was as a nuke-slinging defense interceptor. it was also a 'stealth plane', as is the sr-71 (the sr-71 has a transponder they have to switch on to help control towers see them to direct their landing pattern).
The YF-12 is still treated by the airforce (publicly) as just a trivial test plane that never amounted to anything. But they built nearly a hundred of them, which with 4 nukes apiece that's quite a lot of firepower for "testing". They were retired at an unknown time (they were never officially operational), and most of them have been cannibalized for spare sr-71 parts (which is now also decommissioned).
The YF-12 may have been part of why the US unflinchingly signed the Anti-Ballistic Missile Treaty in 1972.
If the SR-71 (and YF-12) were still in service, it would *still* "fly so fast, so high, nothing could touch it" as you put it.
The ongoing treatment of the YF-12 as an unimportant aircraft by the AF, strongly suggests a replacement plane with a somewhat similar mission profile is currently in service, or is at least still a twinkle in the eye of AF black budget types.
Of course, some of the above, is rather "unofficial".
(daddy was an aerospace worker who didn't have a son to fill with aerospace/military trivia. I was a bored geeky girl with a voracious appetite for reading, who just sponges up knowledge if it's interesting at all.)