Russia's recent aggression against Ukraine has disrupted nearly a generation of relative peace and stability between Moscow and its Western neighbors and raised concerns about its larger intentions. From the perspective of the North Atlantic Treaty Organization (NATO), the threat to the three Baltic republics of Estonia, Latvia, and Lithuania — former Soviet republics, now member states that border Russian territory — may be the most problematic of these. In a series of war games conducted between summer 2014 and spring 2015, RAND Arroyo Center examined the shape and probable outcome of a near-term Russian invasion of the Baltic states. The games' findings are unambiguous: As presently postured, NATO cannot successfully defend the territory of its most exposed members. Fortunately, it will not require Herculean effort to avoid such a failure. Further gaming indicates that a force of about seven brigades, including three heavy armored brigades — adequately supported by airpower, land-based fires, and other enablers on the ground and ready to fight at the onset of hostilities — could suffice to prevent the rapid overrun of the Baltic states.

Key Findings

As Presently Postured, NATO Cannot Successfully Defend the Territory of its Most Exposed Members

Across multiple games using a wide range of expert participants in and out of uniform playing both sides, the longest it has taken Russian forces to reach the outskirts of the Estonian and/or Latvian capitals of Tallinn and Riga, respectively, is 60 hours.
Such a rapid defeat would leave NATO with a limited number of options, all bad.

It Is Possible to Avoid Such Consequences

A force of about seven brigades, including three heavy armored brigades — adequately supported by airpower, land-based fires, and other enablers on the ground and ready to fight at the onset of hostilities — could suffice to prevent the rapid overrun of the Baltic states.
While not sufficient to mount a sustained defense of the region or to achieve NATO's ultimate end state of restoring its members' territorial integrity, such a posture would fundamentally change the strategic picture as seen from Moscow.

The Expense Needs to Be Balanced Against the Consequences of Not Rethinking the Current Posture

While this deterrent posture would not be inexpensive in absolute terms, it is not unaffordable, especially in comparison with the potential costs of failing to defend NATO's most exposed and vulnerable allies.