A-12s (CIA variant) and YF-12As (Air Force variant) at Groom Lake in 1964. The early versions were mostly bare titanium with only the leading edges painted with the black paint, the function of which was to radiate heat away from the areas exposed to the highest temperatures. These models can be distinguished from the later SR-71s by the lack of a chine carried all the way to the nose of the aircraft; these have the original conical nose.
The second one back is a trainer, with the second cockpit visible.
I find it totally amazing that these were designed with slide rules.