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On Monday, 22 February, Russia filed a request to fly a spy plane loaded with surveillance equipment over the United States. To the uninformed, the request may sound bizarre, but it comes as part of the Treaty on Open Skies, which was approved in 1992 and came into effect in 2002. According to the treaty. Signatories are allowed to fly unarmed aircraft – equipped with still, video, and infrared cameras, as well as certain types of radar – over the territory of other treaty members. All planes are inspected to make sure the equipment does conforms to particular power restrictions.

The purpose of the treaty, explains Pentagon spokesman Capt Jeff Davis, is to prevent military escalation by allowing signatories to ascertain the nature of military movements.

“We have to remember that while we have pretty good intelligence on a lot of the world, a lot of other countries don’t necessarily have that great of intelligence on us,” Davis said. “So, in the interest of transparency and [avoiding] miscalculation on their part, sometimes it’s worthwhile to allow them to have a look at what you’re doing or what you’re not doing.”

Both the US and Russia have “done it many times before,” Davis said.

The policy is not without critics. Admiral Cecil Haney, chief of US Strategic Command, in a letter to Congressman Mike Rogers, opines that the exploitation of the treaty has become part of Russian intelligence gathering practices.

“In addition to overflying military installations, Russian Open Skies flights can overfly and collect on Department of Defense and national security or national critical infrastructure,” wrote Haney. “The vulnerability exposed by exploitation of this data and costs of mitigation are increasingly difficult to characterize.”

The treaty was codified in a time of film and unsophisticated equipment, and may have reached a point where it needs to be reconsidered. Treaty members have examined how to modernise it, but so far it remains adapted to technology nearly a quarter century old.