There was an earlier version built for the CIA, the 12/Archangel.
The link below is a fascinating history of this CIA earlier model of the SR71.
WOW!
Lots of ‘good stuff’!
Wing panels that were spot welded
in the summer failed within six or seven weeks, but
those made in the winter lasted indefinitely. The
problem was traced to Burbank’s water, which was
heavily chlorinated in the summer to prevent algae
growth but not in the winter. Switching to distilled
water to wash the panels after acid treatment
prevented a recurrence. When bolt heads dropped
off under high heat, Skunk Works troubleshooters
found that cadmium-plated wrenches left enough
residue to weaken the fittings. Hundreds of tool
boxes had to be inspected to get rid of the nowuseless
implements.
A modified version of an engine designed for
another program four years earlier, the jet generated as much power as the turbines
of the ocean liner the Queen Mary.—160,000 horsepower
or over 32,000 pounds of thrust.
Rich and his colleagues did
much of the testing in wind tunnels at a NASA facility
in northern California. They had to work mostly at
night because the tests drained too much electricity
from the local power grid during the day.
On the second pass toward
Hanoi and Haiphong from the west, at least six
missiles were fired from sites around the capital. The
A-12 was flying at Mach 3.1 at 84,000 feet. Looking
out the rear-view periscope, Sullivan reported
seeing six vapor trails go up to about 90,000 feet
behind the aircraft, arc over, and begin converging
on it. He saw four missiles—one as close as 100
to 200 yards away—and three detonations behind
the A-12. Six missile contrails appeared on mission
photography.