As NATO expanded eastwards after the Cold War, the geography that the Alliance needed to defend changed significantly (See map). Rather than a relatively narrow front in Central Europe (dashed line), NATO now had to contend with a far wider front across Eastern Europe (solid line) stretching its defense capabilities. When the Baltic countries of Estonia, Latvia, and Lithuania joined the Alliance in 2004, they created an even greater operational challenge for NATO.
Lay of the Land
Sitting on the Alliance’s eastern edge, all three Baltic countries border Russia, NATO’s most likely adversary. But only one, Lithuania, is connected to any other NATO country. Lithuania’s border with Poland, just 100 km wide and with a single highway running through it, forms a bottleneck that NATO planners call the Suwalki Gap (named after a nearby Polish town). Worse still, on one side of the gap is Kaliningrad, a large Russian military enclave, and on the other side is Belarus, a close Russian ally.
Figuring out how to overcome that problematic geography became more pressing for NATO after 2007, when Russia suspended its participation in the Conventional Armed Forces in Europe treaty, which had limited the number of troops and equipment that NATO and Russia could station in continental Europe. Since then, Russia has steadily strengthened its military forces across its western regions, including Kaliningrad. One recent study estimates that if Russia were to invade the Baltics today it could mobilize 25 battalions of armor, airborne, and mechanized infantry (supported by ten battalions of artillery, six of attack helicopters, and five of short-range ballistic missiles). By contrast, the Baltic countries could field only 11 battalions of light infantry, most of which are reserve units. Plus, without any fighter aircraft of their own, Baltic forces would be completely exposed to Russian air power.
Clearly, without NATO support, the Baltics could offer little serious resistance to a Russian invasion. From St. Petersburg, a Russian column could advance into Estonia to seize Tallinn. From Pskov, another column could advance into Latvia to take Riga and pivot south into Lithuania. Simultaneously, Russian forces in Kaliningrad could seal off likely avenues for NATO reinforcements. A Russian thrust toward Marijampolė would close the Suwalki Gap and another toward Klaipėda would close NATO’s most accessible Baltic port. To ensure battlefield success, Russia could use its strategic reserve of airborne and Spetsnaz forces.
From the Sea
Should Russia sever the land and air routes into the Baltics, NATO may be forced to send its reinforcements across the Baltic Sea. However, doing so would face serious hurdles. First, NATO lacks enough military sealift to transport the volume of troops and equipment necessary to stop a Russian assault. As a work-around for its sealift shortage, NATO could commandeer car ferries and other civilian shipping. But NATO could not as easily work around the threat of Russian long-range anti-ship cruise missiles. Launched from K-300P Bastion-P coastal defense batteries in Kaliningrad, such missiles could inflict heavy casualties on any NATO reinforcements.
Since the U.S. Navy would not likely want to expose an aircraft carrier battle group to such a threat in the confined waters of the Baltic Sea, the job of escorting NATO’s troop transports would then fall on smaller warships with less sophisticated anti-ship cruise missile defenses. That could put already scarce troop transports at higher risk.
Even worse, if Russian forces were to capture all the ports in the Baltics, NATO might have to mount an amphibious assault to reestablish itself on land. That would be difficult to pull off, despite the spectacle of NATO’s Baltic Operations (Baltops) exercises. Amphibious assaults have never been easy; but they are even more difficult today, given that modern precision-guided munitions could make short work of landing craft, helicopters, and even MV-22 aircraft.
Given the potential for Russia to interdict their seaborne forces, NATO commanders would naturally want to suppress Russian coastal defense batteries. After all, a successful missile strike on a single transport could result in the loss of hundreds of troops and their equipment. Multiple missile strikes could swiftly sap the combat strength of any NATO relief force.
At first glance, the suppression of Russian coastal defense batteries (and the air defense systems protecting them) would appear to be a straightforward affair. NATO air forces based in Germany and Poland could easily reach and strike Russian positions in Kaliningrad. However, were NATO air forces to do so, they would be hitting targets on Russian soil. That, in turn, could prompt Russia to expand the conflict beyond the Baltics. NATO could expect retaliatory Russian strikes on its German and Polish air bases.
In addition, one could reasonably expect NATO commanders to want to stem the flow of Russian forces and supplies into the Baltics, either to slow a Russian invasion or as a prelude to a NATO counteroffensive. To be most effective, that would require NATO strikes on Russian logistical facilities near St. Petersburg and Pskov. Such strikes would hit targets deep into Russian territory. That could also prompt Russia to escalate. It could launch retaliatory strikes against NATO logistical facilities in Antwerp, Hamburg, and Rotterdam. Russia could even use submarine-launched land-attack cruise missiles to hit targets in the United States, like Naval Station Norfolk or Pope Air Force Base, which normally support U.S. operations abroad.
Ultimately, Russia could threaten to use nuclear weapons. Indeed, in 2016, Russia moved Iskander 9K720 intermediate-range nuclear-capable missiles into Kaliningrad. It may have done so, in part, to ensure that NATO leaders think twice before attacking targets there, since a strike on Russian nuclear forces could quickly escalate into a nuclear confrontation. In any case, even if armed with conventional warheads, those missiles could hit and devastate targets as far away as Germany.
The best way for NATO to overcome its operational challenge in the Baltics is to make sure it never manifests itself. To do that, NATO must convince Russia that it could not achieve a quick victory in the region. Already NATO has rotated small air and ground detachments through the Baltic countries to stiffen their defenses as well as to create a tripwire to guarantee a forceful NATO response in case of a Russian attack.
But more needs to be done before Russia is really convinced. Forward-deployed NATO battle groups need to be stronger—strong enough to hold open avenues for NATO reinforcements. Moreover, NATO countries need to revive their conventional war-fighting capabilities and maintain them at a higher state of combat readiness than they do now. Finally, NATO forces need to be able to react more quickly to Russian actions. That means Western governments need to give NATO’s commander the authority to not only put their national military forces on alert, but also order them into the field for limited periods. In short, NATO should, once again, adhere to the old aphorism that “if you want peace, prepare for war.”
 David A. Shlapak and Michael W. Johnson, Reinforcing Deterrence on NATO’s Eastern Flank: Wargaming the Defense of the Baltics (Santa Monica, CA: RAND, 2016), pp. 4-5.
 Should Belarus allow them to do so, Russian forces could also pass through Belarusian territory to advance on Vilnius from Minsk.
 Brooks Tigner, “Kaliningrad becoming a more dangerous military threat for NATO, say officials,” Jane’s Defence Weekly, Nov. 10, 2016.