1800s - James Clerk Maxwell formulates the electromagnetic theory, which leads to Heinrich Hertz's experiments with electromagnetic radiation. These experiments verified Maxwell's formulas, creating the opportunity to apply them to objects, and provided evidence on how the radiation would scatter when shot at an object.
1904 - Christian Hülsmeyer patents “an obstacle detector and ship navigation device” based on Hertz’s findings, which begins the development of radar.
1930s & 1940s - Rapid worldwide development of radar systems begins, fueling the need for stealthy planes in times of war.
Dec. 1944- The Horten brothers' jet-powered prototype, the Ho IX V2, flies in Germany. World War II ended before the plane could be built, and the project was abandoned. Many doubted that the plane could fly successfully, because of its tailless design.
1946- The giant YB-35 flying-wing bomber finally takes flight. Although the project had been approved in 1941 and scale models had successfully been flown in 1942, the size of the YB-35 pushed back its take-off date to four years later.
1948- The first flight of YB-49, the jet powered version of the YB-35, is conducted. A drive train complication caused the YB-35 program to be cancelled before its military debut, and its jet engine predecessor had little more luck: Some feared the YB-49 plane was too unstable when one of the test flights failed, killing all of its crew. The plane featured four small vertical tailfins, creating the image of a flying arrowhead. Though the two were not considered "stealth" aircraft, their "strategic bomber" design set the foundation for the future stealth bomber, the B-2 Spirit.
1950s- Radar continues to develop slowly, but now includes the use of Doppler frequency, which will later be well-known for its use in police radar guns and weather radars. The first ballistic missile defense radars are developed.
1954- Under a contract with the CIA, Lockheed Aircraft begins to work on the U-2 Spy Plane. The plane was considered stealthy because of its ability to fly at extremely high altitudes, but the Soviet Union's defense radar was still able to detect the aircraft.
1958- The CIA begins the OXCART project, looking for a replacement for the failed U-2 plane. The OXCART was capable of flying at speeds above Mach 3 and, like the U-2, at high altitudes. The OXCART was equipped with materials meant to reduce its signature on radar, from a special fuel to parts of the plane that "trapped" radar energy.
1964- The SR-71 Blackbird– based on the OXCART design– takes its first flight. This long-range reconnaissance plane was also capable of flying at speeds of Mach 3, and remained in service until 1990.
Late 1970s- A stealthy helicopter called The Quiet One is developed during the Vietnam War. The Air Force begins working on the B-2 Spirit stealth bomber, capable of flying more than 6,000 nautical miles and carrying 40,000 lbs.
1977- Lockheed receives a contract from the U.S. Air Force to build the Have Blue. This aircraft used special conductive coatings and airframe surfaces to minimize its radar signature. The plane was kept a top secret, only tested on dark nights in Area 51. The Have Blue was the precursor to the infamous F-117 aircraft.
1980s- Radar improves the ability to distinguish target types from one another, and phased-array radars for Air Defense (Patriot and Aegis systems) enter serial production. Northrop begins developing the Tacit Blue.
1981- Northrop is awarded a contract for the B-2 Spirit stealth bomber. Although much larger, this plane would second the F-117 in stealth abilities. Twenty-one B-2 Spirit bombers would be built and purchased by the U.S. Air Force.
1989- The F-117, one of the most famous and successful stealth aircraft, is revealed. Although its development was kept a secret in the early 1980s, the F-117's beginning came from the Have Blue, and was the first plane to be completely designed around the aspect of stealth.
1997- The F-22 Raptor interceptor completes its first successful flight. Its smooth, curved surfaces are similar to those used in the design of the B-2 Spirit bomber.
2001- Lockheed Martin wins the competition to build the Joint Strike Fighter. When measuring the radar reflectivity of an aircraft, designers compare the reflectivity of an aluminum sphere to the plane's reflectivity. The Joint Strike Fighter has the reflectivity of a golf ball-sized aluminum sphere, where as the earlier B-2 has the radar signature of a marble.