While it is true that the SR-71 & A-12 were spy planes, and that the GP makes a slightly asinine statement, the pedant (and aviation geek) in me feels obliged to point to the YF-12[1].

The YF-12 was a twin-seater derivative of the A-12 that was developed as a fighter aircraft, complete with a look-down/shoot-down radar and missile bays.

The F-12 never made it to production, but a small number high-speed of weapons tests were conducted with the 3 YF-12 airframes that were built.

With that said, the MiG-25 should certainly not be belittled as a marvel of aviation. It was a blisteringly fast interceptor and reconnaissance aircraft, with an impressive radar system for its time. It filled a special role in the Russian Air Force until last year[2].

[1] http://en.wikipedia.org/wiki/Lockheed_YF-12 [2] https://medium.com/war-is-boring/21d12739b5db

Just out of interest, was the MiG-25 'all steel' and 'all valves'? As in no electronics as we know them, just valves? I had heard that it was EMP-proof due to the lack of any transistors on board...

80% nickel steel alloy, 11% aluminium, and 9% titanium. Using valves instead of transistors meant for easier maintenance in addition to resistance to EMP. [0]

[0] http://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-25

The SR-71 and the MiG-25 were originally envisioned for exactly the same role: next-gen high speed, high altitude interceptors. We made a decision that missiles would fill the niche better, and the SR-71 became a recon platform, but it's roots are still in combat.