Project Isinglass

Project Isinglass was the code name given to two heavily classified, crewed reconnaissance aircraft studied by the Central Intelligence Agency (CIA) as potential replacements for the Lockheed A-12 and SR-71 during the mid-1960s. The first proposal under the Isinglass name, a high-altitude plane to fly at Mach 4 – Mach 5 (4,900–6,100 km/h; 3,000–3,800 mph), was considered an insufficient advancement over existing aircraft; the second, much more advanced design, sometimes referred to as Project Rheinberry, was an air-launched, Mach 20 (24,500 km/h; 15,200 mph) rocket-powered boost-glide aircraft that would use a very-high-altitude trajectory to avoid defenses. This aircraft was considered too costly for development, and the project was abandoned in 1967.