Lockheed Have Blue 
demonstrator stealth bomber

Lockheed Have Blue was the code name for Lockheed's proof of concept demonstrator for a stealth bomber. Have Blue was designed by Lockheed's Skunk Works division, and tested at Groom Lake, Nevada. The Have Blue was the first fixed-wing aircraft whose external shape was defined by radar engineering rather than by aerospace engineering. 

The Lockheed Have Blue was born out of a requirement to evade radar detection. During the Vietnam War, radar-guided SAMs and AAA posed a significant threat to US aircraft. For this reason, strike aircraft during the war often required support aircraft to perform combat air patrols and suppression of enemy air defenses (SEAD). The 1973 Yom Kippur War again highlighted the vulnerability of aircraft to SAMs – the Israeli Air Force lost 109 aircraft in 18 days. During the Cold War, the 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.Wiki Link