According to Jacobsen this photo depicts an A-12 Oxcart hidden behind a barrier at Area 51.
She writes, “It took 2,400 Lockheed Skunk Works machinists and mechanics to get a fleet of 15 ready for the CIA. Visible on either side of the aircraft are the uniquely adjustable inlet cones that regulated airflow and allowed the CIA spy plane to cruise in the afterburner and reach peak speeds of Mach 3.29 by May 1965.”
