Soviet Union developed an integrated defense network, central to which were medium- to long-range surveillance radars. SAMs and AAAs would be set up around key locations to defend them from incoming enemy aircraft. If the loss ratio of Israel during the Yom Kippur War was experienced by NATO forces during a military confrontation with the Warsaw Pact, NATO aircraft numbers would be depleted within two weeks. In 1974, DARPA secretly requested answers from five aircraft manufacturers regarding two considerations. The first was about the signature thresholds at which an aircraft is virtually undetectable. The second point was whether these companies had the capability to design and manufacture such an aircraft. Fairchild and Grumman declined to participate, while General Dynamics insisted on the use of electronic countermeasures. As a result, General Dynamics left the discussion. The remaining two companies, McDonnell Douglas and Northrop, were each awarded $100,000 for further research. Design effort and early testing Lockheed, having been absent from the fighter aircraft industry for 10 years, was not approached by DARPA in 1974. Ed Martin, Lockheed California Companies director of science and engineering, became aware of the research into stealth during his work at the Pentagon and Wright-Patterson AFB. Martin and Ben Rich, who at that time had recently become Skunk Works' president, briefed Clarence "Kelly" Johnson on the program. The Central Intelligence Agency (CIA) gave Skunk Works permission to discuss with DARPA the stealth characteristics of the A-12, M-21 and D-21. On behalf of the company, Rich and Martin formally requested permission from DARPA to participate in the program, but the agency initially refused because there were insufficient funds; after much debate, Lockheed was allowed entry, albeit without a government contract. Preliminary designer Dick Scherrer requested possible shapes upon which he could base his low radar cross-section (RCS) design. He was introduced to Denys Overholser, who recommended an aircraft with flat surfaces. Overholser later recounted his discussion with Sherrer: "When Dick Scherrer asked me ... I said 'Well, it's simple, you just make it out of flat surfaces, and tilt those flat surfaces over, sweeping the edges away from the radar view angle, and that way you basically cause the energy to reflect away from the radar.'" Scherrer subsequently drew a preliminary low-RCS aircraft with faceted surfaces. At the same time, Overholser hired mathematician Bill Schroeder, with whom he had a prior working relationship – in fact, it was