The Treaty on Open Skies: Observation Flights Between Rivals

Not to be confused with commercial Open Skies agreements, the Treaty on Open Skies allowed rival militaries to fly unarmed observation missions over one another's territory.

Eisenhower's idea

At the 1955 Geneva summit, President Dwight D. Eisenhower proposed that the United States and the Soviet Union allow each other to conduct aerial reconnaissance flights, reducing the fear of surprise attack. The Soviet Union rejected the proposal, and the idea lay dormant for decades.

Revival and signature

President George H. W. Bush revived the concept in 1989. Negotiated among members of NATO and the Warsaw Pact, the treaty was signed in Helsinki on March 24, 1992, and entered into force on January 1, 2002.

How it worked

States parties were allotted quotas of observation flights over one another's territory. Aircraft carried agreed sensors, and the observed state could have personnel aboard. Imagery could be shared among parties. The goal was confidence: every party, regardless of size, gained a direct way to see military activity of concern.

The United States flew its missions with the OC-135B Open Skies, a modified aircraft from the C-135 family.

Withdrawal

The United States gave notice of withdrawal in May 2020, citing Russian violations, and its withdrawal took effect on November 22, 2020. Russia announced its intention to withdraw in January 2021 and formally left in December 2021. The treaty remains in force among its remaining parties.

Why it matters

The treaty is a case study in how aviation can serve diplomacy directly: aircraft as instruments of transparency rather than force.