it to specifications for the expected altitude of the plane and using new anti-vibration and mounting techniques. This camera became the A-1. Once that work was underway, Baker used his pioneering algorithms to perform ray tracing, calculating paths on the IBM CPC at Boston University. This produced the A-2 camera, containing three K-38 cameras with 24-inch f/8.0 lenses. Next, Baker and Scott began work on the A-2B. This would use a larger f/10 aspheric lens. This single camera would provide configurable coverage up to horizon-to-horizon. The A-2C folded f/20 system was rejected by Lockheed's Kelly Johnson, as it was larger than the available space. Other 'C' camera designs were unsuccessful. After 1950, Soviet air defenses consistently intercepted all aircraft near the country's borders—sometimes even those in Japanese airspace. Existing US reconnaissance aircraft, primarily bombers converted for reconnaissance duty such as the Boeing RB-47, were vulnerable to anti-aircraft artillery, missiles, and fighters. Richard Leghorn of the United States Air Force suggested that an aircraft that could fly at should be safe from the MiG-17, the Soviet Union's best interceptor aircraft, which could barely reach . He and others believed that Soviet radar, which used American equipment provided during the war, could not track aircraft above . At the time, the highest-flying aircraft available to the US and its allies was the English Electric Canberra, which could reach . The British had already produced the PR3 photo-reconnaissance variant, but the USAF asked for English Electric's help to further modify the American-licensed version of the Canberra, the Martin B-57, with long, narrow wings, new engines, and a lighter airframe to reach . The U.S. Air Research and Development Command mandated design changes that made the aircraft more durable for combat, but the resulting RB-57D aircraft of 1955 could only reach . The Soviet Union, unlike the United States and Britain, had improved radar technology after the war, and could track aircraft above . Lockheed proposal It was thought that an aircraft that could fly at would be beyond the reach of Soviet fighters, missiles, and radar. Another Air Force officer, John Seaberg, wrote a request for proposal in 1953 for an aircraft that could reach over a target with of operational radius. The USAF decided to solicit designs only from smaller aircraft companies that could give the project more attention. Under the code name "Bald Eagle", it gave contracts to Bell Aircraft, Martin