Supersonic Gusto

The dichotomy was the relationship between “stealth” and performance, and this would be a recurring theme throughout Johnson’s design submissions for a U‑2 replacement. A conventional design was most likely to deliver the required performance, but these criteria often proved to be too easily detected by radar; whereas a design emphasizing stealth struggled to deliver the prerequisite performance. Johnson was also concerned at the speed of Soviet radar development which, coupled with the inevitable use of more diverse radar frequencies, would, he was convinced, further complicate the search for a panacea to these conflicting paradigms. Therefore on April 21, 1958, probably as a hedge against these problems, Johnson began sketching his first Mach 3 design for the Agency. As with his Suntan design for the Air Force, this primarily put extreme speed and altitude performance at the heart of vehicle “survivability,” rather than stealth. He named the design in his notebook “U‑3” (this notebook would subsequently become known as his “Archangel” notebook – Skunk Works insiders often referred to the highflying U‑2 as “Kelly’s Angel,” but as this new design represented another performance leap, “Archangel” seemed the logical extension). He also recorded the basic design requirements and his preference for choosing two higher thrust‑to‑weight ratio J58 engines over the J93. Then over a number of days, he continued to refine and further investigate the high‑speed design, before reporting his findings to Bissell.

^{Johnson proposed that his Archangel I design be powered by two J58s and built from titanium B 12 °CVA. Together with Gusto 2A, the designs were received with interest by Dr Richard Bissell, the DCI’s Special Assistant for Planning and Coordination, but would come to nothing. (Lockheed Martin)}

A team from the SEI conducted a blip‑scan analysis of Johnson’s U‑3 proposal. By taking into account the design’s speed, altitude, and RCS, they were able to evaluate the dwell time (the length of time the aircraft remained within a radar beam) and therefore its probability of detection. Three different frequency bands – 70, 600, and 3,000 megacycles per second – were considered in these computations and the subsequent report was highly significant; becoming known as the “Blip‑Scan Study,” it set specific performance targets for the U‑2 follow‑on: a speed of Mach 3, an altitude of 90,000ft, and an RCS of not more than 10m² and preferably less than 5m².