The Open Skies Treaty and Prospects for European Confidence-Building Measures

Main Image Credit A US Air Force OC-135B Open Skies.

Officials from Donald Trump’s administration have now announced that the US will formally withdraw in six months from the Open Skies Treaty. The viability of multilateral confidence- and security-building measures is called into question.

The 1992 Open Skies Treaty might be a comparatively obscure measure to the average person in Western audiences, but US participation has always been critical to its functioning, and its effective dissolution would mark yet another blow to the post-Cold War international security framework. While the US withdrawal from the Intermediate-Range Nuclear Forces Treaty was the most high-profile gesture from Donald Trump’s administration, it was one in a series of withdrawals from agreements which provide the main pillars of the arms control regime.


There are qualities to the treaty, which was designed to allow unarmed aerial surveillance flights over the entire territory of its participants in order to enhance mutual understanding and confidence, that make it a comparatively easy target for critics. Most obviously, it is of limited scale. According to the official fact sheet, ‘The Russian Federation and the United States each have an annual passive quota of 42 [observation flights], while the other States Parties have quotas of 12 or fewer’. So, this is hardly a comprehensive monitoring, but a fleeting one.

The US has two ageing OC-135B aircraft dedicated to the task, both constructed in 1961 and still using analogue mission equipment. The aircraft are barely flyable and are potentially dangerous to their crews; conducting observation flights is routinely impeded by maintenance problems. The US has also yet to transition the aircrafts’ cameras away from wet film photography to digital equipment due to a lack of funds. And although the Russians were the first to transition to modern digital photography, they only did so in 2016. With so few flights using outdated equipment, observation activity conducted under the treaty is clearly inferior to the capacity of satellites to observe territory, and the advances made in satellite technology since the treaty was initially ratified mean that scrapping it will make little practical difference to the major signatories of the treaty. There is, therefore, some merit to the argument that the Open Skies Treaty has outlived its usefulness.

Russian Obstruction

Additionally, the Open Skies Treaty was subjected to Russian obstructionism. Moscow has undermined the confidence-building mechanisms within the treaty by using bureaucratic arguments to deny observation aircraft the right to over-fly Kaliningrad, Abkhazia and South Ossetia (the latter two, disputed Georgian territories occupied by Russian troops and proxies), and have often restricted or denied the use of their airfields. Furthermore, a number of signatories to the treaty collectively conducted missions over southwestern Russia and Ukraine at the time of the 2014 Russian military incursion into Ukraine took place, establishing a more complete understanding of the situation as a result. This led to fears that Moscow will take further steps to ensure the treaty is not used over a conflict zone such as this again.

There have also been worrying allegations that Russia might use their overflights to map American infrastructure for offensive targeting purposes. While it is true that flights could collect imagery that could contribute to targeting efforts, in practical terms this is a less serious accusation. Given the alternative capabilities available to Russia to collect similar imagery, the treaty is unlikely to place the US or its allies at increased risk.

Enduring Value

Nevertheless, Open Skies used to enjoy support from within the US political and defence establishments. In May 2018, then Secretary of Defense James Mattis wrote to Republican Nevada Senator Deb Fischer, ‘it is in our Nation’s best interest to remain a party to the Open Skies Treaty’, a response to her comments about Russia undermining the treaty. Former US ambassador to Ukraine, Steven Pifer, recently noted that ‘It’s really hard to see what we would gain from withdrawing from the treaty … [w]e actually conduct many more flights over Russia than Russia conducts over the United States’. Experts in the field, such as Olga Oliker from the International Crisis Group, also believe withdrawing from the treaty is not in the US’s best interests.

The Open Skies Treaty is widely considered one of the pillars of European security arrangements, along with the Treaty on Conventional Armed Forces in Europe (CFE) and the Vienna Document on Confidence- and Security-Building Measures (often shortened to the Vienna Document). However, the CFE Treaty, which sets numerical limitations of signatories’ conventional vehicle and weapon inventories, was effectively terminated when Russia withdrew in 2015 over the ongoing dispute regarding its role in the conflicts in Georgia and Ukraine, and now the Open Skies Treaty looks to be going as well.

And that will be a pity for although general confidence- and security-building are the main features of the treaty, it is the information-sharing provisions that make the Open Skies Treaty unique. Under the treaty, states are not only allowed to ‘conduct short-notice, unarmed, reconnaissance flights over the others' entire territories to collect data on military forces and activities’, but also that states can request that information at cost. Should the US withdraw from the agreement, the lost observation capacity which Washington would forfeit would mean little to the US but, with the treaty’s collapse, it would leave more-exposed states such as Ukraine in a vulnerable position. Furthermore, smaller states lack advanced observation satellites and can suffer from poor situational awareness. Information gathered under the treaty has compensated for this in the past by, for instance, assisting in conflict monitoring since the Russian invasion of Ukraine. All that could now be gone.

If the treaty collapses, be it through Russian recalcitrance or the gesture of the US withdrawal, the indirect result will undermine the security of minor signatories. And it is not at all obvious that European states would be able to negotiate a similar substitute arrangement in the future.

What is Left Standing?

Yet despite the tendency of the Trump administration to dismiss international agreements as unimportant or detrimental to US interests, some confidence- and security-building measures look set to remain in place for the foreseeable future. The Vienna Document — the last of the European security troika — has so far avoided any serious calls for withdrawal from its signatories, though as with the Open Skies Treaty, it is in serious need of reform.

The provisions of the Vienna Document, which place limitations on snap exercises and detail the thresholds for notifying other states of military exercises, are outdated. Currently, notification thresholds apply to exercises involving 9,000 personnel, 250 Main Battle Tanks, 500 Armoured Combat Vehicles or 250 Self-Propelled Artillery/Multiple Launch Rocket System platforms. Yet in an era of decreasing forces sizes but with formations and platforms being increasingly capable and lethal, snap exercises below the threshold of notification are still of a scale where they cause alarm and can damage relations between neighbours. Nevertheless, the Vienna Document, as one of the surviving security cooperation treaties between Russia, the US and Europe, remains of enduring symbolic and practical importance, as it provides a framework for dialogue and cooperation at a time when any at-scale military activity is greeted with immediate suspicion and mistrust.

Perhaps the worst consequence of the US withdrawal from the Open Skies Treaty will be to further reinforce the narrative that the US no longer cares about multilateral security cooperation. And that is bad enough.

Sarah Martin works on human rights in Eurasia in Washington, DC, and was formerly a Research Assistant at the Secretariat of the Organization for Security and Co-operation in Europe Parliamentary Assembly.

Nick Reynolds is the Research Analyst for Land Warfare at RUSI.

The views expressed in this Commentary are the author's, and do not represent those of RUSI or any other institution.


Sarah Martin

View profile

Nick Reynolds

Research Fellow, Land Warfare

Military Sciences

View profile


Explore our related content