Boeing OC-135W Open Skies out of DC.

The OC-135B Open Skies United States Air Force observation aircraft supports the Treaty on Open Skies.

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The Treaty on Open Skies entered into force on January 1, 2002, and currently has 34 party states. It establishes a program of unarmed aerial surveillance flights over the entire territory of its participants. The treaty is designed to enhance mutual understanding and confidence by giving all participants, regardless of size, a direct role in gathering information about military forces and activities of concern to them. Open Skies is one of the most wide-ranging international efforts to date promoting openness and transparency of military forces and activities. The concept of "mutual aerial observation" was initially proposed to Soviet Premier Nikolai Bulganin at the Geneva Conference of 1955 by President Dwight D. Eisenhower; however, the Soviets promptly rejected the concept and it lay dormant for several years. The treaty was eventually signed as an initiative of US president (and former Director of Central Intelligence) George H. W. Bush in 1989. Negotiated by the then-members of NATO and the Warsaw Pact, the agreement was signed in Helsinki, Finland, on March 24, 1992.