[1] After overflights began and the Soviets demonstrated the ability to track and attempt to intercept the U-2, this estimate was adjusted downward.

[2] To extend the life of the U-2, the CIA implemented Project Rainbow, which added various countermeasures to confuse Soviet radars and make interception more difficult.

The weight of the equipment lowered the aircraft's maximum cruise altitude, making it more vulnerable to interception.

[3] As early as 1956 Bissell had already started looking for an entirely new aircraft to replace the U-2, with an emphasis on reducing the radar cross-section (RCS) as much as possible.

Returns from real targets, like an aircraft, would become visible as multiple radar pulses all drawn onto the same location on the screen, and produced a single, brighter spot.

By 1957 so many ideas had been submitted that Bissell arranged for the formation of a new advisory committee to study the concepts, led by Edwin H. Land under the designation Project Gusto.

The Navy introduced a submarine-launched inflatable rubber vehicle that would be lifted to altitude by a balloon, boosted to speed by rockets, and then cruise using ramjets.

Code-named FISH or First Invisible Super Hustler, the aircraft was based on a lifting body design that bears some resemblance to the ASSET spacecraft of a few years later.

It differed in having the nose taper down to a flat horizontal line instead of the rounded delta of the ASSET, and the fuselage was not as large at the rear.

To endure the intense heat generated by aerodynamic heating at these speeds, the leading edges of the nose and wings were built of a new "pyroceram" ceramic material, while the rest of the fuselage was made of a honeycomb structure stainless steel similar to the material for the proposed XB-70 Valkyrie.

The committee did not find either entry particularly interesting, and when the B-58B was cancelled by the Air Force in 1959, the entire FISH concept was put in jeopardy.

The intakes and exhausts were arranged to reduce radar cross section, and the entire aircraft had the same sort of angular appearance as the later Lockheed F-117.

The leading edges of the wings and intakes continued to use pyroceram, while other sections used a variety of materials selected for low radar reflection, including fiberglass.

In July 1959, Lockheed and Convair presented preliminary designs and cross selection estimates to the review panel.

[6][7] In addition, since the spoofing relied on deficiencies in the radar display systems, upgrading them could render the entire concept moot.

The failure of the A-12's attempts to avoid radar was demonstrated when the Vietnamese proved able to track the A-12 with some ease, firing on several of them and causing minor damage on one occasion in 1967.