Stealth Technology - History

History

In England, irregular units of gamekeepers in the 17th century were the first to adopt drab colours (common in 16th century Irish units) as a form of camouflage, following examples from the continent.

Diffused lighting camouflage, a shipborne form of counter-illumination camouflage, was trialled by the Royal Canadian Navy from 1941 to 1943. The concept was followed up, but for aircraft, by the Americans and the British: in 1945 a Grumman Avenger with Yehudi lights, reached 3,000 yards (2,700 m) from a ship before being sighted. This ability was rendered obsolete by radar.

The U-boat U-480 may have been the first stealth submarine. It featured a anechoic tile rubber coating, one layer of which contained circular air pockets to defeat ASDIC sonar. Radar absorbent rubber/semiconductor composite paints were used by the Kriegsmarine on submarines in World War II. Tests showed they were effective in reducing radar signatures at both short (centimetres) and long (1.5 metre) wavelengths.

One of the earliest stealth aircraft seems to have been the Horten Ho 229 flying wing. It included carbon powder in the glue to absorb radio waves. Some prototypes were built, but it was never used in action.

During the 1950s, the Avro Vulcan, a British bomber, had a remarkably small appearance on radar despite its large size, and occasionally disappeared from radar screens entirely.

In 1958, the CIA requested funding for a reconnaissance aircraft to replace U-2 spy planes and Lockheed secured contractual rights to produce it. "Kelly" Johnson and his team at Lockheed's Skunk Works were assigned to produce the A-12 (or OXCART), the first of the previously top secret Blackbird series, which operated at high altitude of 70,000 to 80,000 ft and speed of Mach 3.2 to avoid radar detection. Radar absorbent material had already been introduced on U-2 spy planes, and various plane shapes designed to reduce radar detection had been developed in earlier prototypes, named A1 to A11. Later, in 1964, an optimal plane shape taking into account compactness was developed and resulted in another "Blackbird", the SR-71. This aircraft surpassed prior models in both altitude (90,000 ft) and speed (Mach 3.3). The Lockheed SR-71 included a number of stealthy features, notably its canted vertical stabilizers, the use of composite materials in key locations, and the overall finish in radar absorbing paint.

During the 1970s the U.S. Department of Defence launched project Have Blue, with the aim of developing a stealth fighter. There was fierce bidding between Lockheed and Northrop to secure the multi-billion dollar contract. Lockheed incorporated into its bid a text written by the Soviet/Russian physicist Pyotr Ufimtsev from 1962, titled Method of Edge Waves in the Physical Theory of Diffraction, Soviet Radio, Moscow, 1962. In 1971 this book was translated into English with the same title by U.S. Air Force, Foreign Technology Division. The theory played a critical role in the design of American stealth-aircraft F-117 and B-2. Equations outlined in the paper could quantify how a plane's shape might minimise its detection by radar, or radar cross-section (RCS), and this was applied by Lockheed in computer simulation to design a shape they called the Hopeless Diamond, securing contractual rights to mass produce the F-117 Nighthawk.

The F-117 project began in 1975 with a model called "The Hopeless Diamond" (a wordplay on the Hope Diamond) due to its bizarre appearance. In 1977 Lockheed produced two 60% scale models under the Have Blue contract. The Have Blue program was a stealth technology demonstrator that lasted from 1976 to 1979. The success of Have Blue led the Air Force to create the Senior Trend program which developed the F-117.