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The three Baltic states jointly announced on Jan. 19, 2024, their intention to build a defensive line along their borders with Russia and Belarus. Initial details are scarce. The defensive line will not include coastal defenses — Baltic coasts will be defended against the Russian Baltic Sea Fleet in other ways, such as anti-ship missile capabilities and sea mines. Estonia, which divulged the greatest amount of detail, estimated that it would build 600 bunkers, together with support points and distribution lines, for a cost of €60 million starting in 2025. There are no plans to place mines, barbed wire, or dragon’s teeth (anti-tank defenses) during peacetime, although the necessary supplies are anticipated to be held in local reserve for quick deployment if and when necessary. At the very least, Estonia also anticipates some difficulties in situating bunkers on private land near the border, which will take time and negotiation with potentially thousands of landowners to resolve. A Baltic defensive line is a huge project. It is worth reflecting on its origins, challenges, and operational-strategic implications. The Baltic ministers of defense identified two primary points of origin for such a defensive line. First is NATO’s communiqué from the 2023 Madrid Summit, which confirmed that the alliance would fight for every meter of its ground. The proposed defensive line reflects a Baltic intention to take this pledge seriously. Second, the Baltic defense ministers also pointed to their lack of substantial geographical depth. The Baltic states believe that they cannot give up ground, which means recognizing that they need to be prepared to contest a Russian invasion from the first moments following the violation of Baltic borders. An obvious third point may also be added: In the face of Russian genocidal atrocities in Ukraine, Baltic governments cannot be seen to be abandoning their populations to the Russians, nor do they want to do so. In Ukraine, the Russians have committed multiple known mass murders (such as at Bucha and Izyum), they have kidnapped children and fast-tracked their adoption and citizenship in Russia, and they are already settling new colonizers on occupied land, especially in the cities. Any one of these is fundamentally unacceptable, and Russia is actively pursuing all three. For the Baltic states, giving up land means giving up people — especially for Estonia and Lithuania, which have substantial population centers on or not far from the border, such as Narva and Vilnius. In this specific regard, Latvia is slightly better placed as its easternmost province of Latgale is also one of the most sparsely populated, with an overall population density of 46 per square mile. Challenges for the defensive line are substantial. First are the lengths of each national border. Estonia’s hostile border is the shortest at 183 miles, most of which is covered by Lakes Peipus and Pihkva or strengthened by the Narva River. Latvia’s borders with Russia and Belarus are 133 and 107 miles, respectively, bereft of natural boundaries. Lithuania’s borders are the longest, reaching nearly 422 miles with Belarus and nearly 171 miles with Russia’s Kaliningrad oblast. These are substantial distances. Estonia’s planned 600 bunkers, likely to be concentrated on the 129 miles of border north and south of Lake Peipus, suggest a density of four to five bunkers per linear mile — yet defensive lines are not simply built linearly but also in depth. Nonetheless, Latvia would need to build 1,116 bunkers and Lithuania 2,758 at similar densities. Bunkers are stationary objects whose effectiveness decreases the better their exact positions are known. The defensive line is likely to incur a challenge to Baltic counterintelligence to prevent Russia from identifying bunker locations in overly substantial detail. However, bunker density is unlikely to be consistent along the entire combined Baltic border as not every part of the border is equally useful for Russian invasion, which necessarily requires roads and railways. Again, Estonia is best placed. North of Lake Peipus, there is only a single crossing point over the Narva River at Narva itself, although there are roads on the Russian side of the river that would enable some degree of near-and even cross-river Russian logistical sustainment. South of Lake Peipus are two major roads and one rail crossing, but also a handful of minor cross-border roads could be used to distribute advancing Russian forces across a broader front. Latvia has one rail and two major road crossings apiece with both Russia and Belarus, along with at least a handful of minor roads directly crossing the border and other Russian roads leading to or running alongside the border. Lithuania has two rail crossings apiece with both Russia and Belarus, along with up to seven major road crossings, two with Russia and five with Belarus, besides various minor roads as well. These are places where bunkers are likely to be concentrated. It is unrealistic to sustain major operations nearly, if not actually, totally off-road. The final challenge is bunker placement in a tactical sense. It seems unlikely for bunkers to be within line of sight from the far side of the Baltic borders, merely giving Russians a chance to scout them during peacetime without danger or even controversy. Higher ground is generally more tactically advantageous than lower ground, and bunkers positioned to generate enfilading fire and be mutually supporting rather than isolated from one another are preferable. While Russian logistical demands lead to a focus on roads and rail, the same is true for Baltic and NATO forces; units fighting on the defensive line have to be logistically sustained as well. These are all lower-level details that will be crucial to the success of the defensive line in case of actual invasion. Finally, what are the operational-strategic implications of the defensive line once it is built? First, it runs counter to the doctrinally preferred Western — and especially American — defensive posture, which is an operationally elastic defense premised upon maneuver warfare. In maneuver defense, terrain (and, by implication, the people populating that terrain) is not valued highly in an operational sense; the land is to be given up if necessary and then recaptured later in the course of counterattacks. The main premise is to engineer the best circumstances in which to destroy advancing enemy forces with as disproportionately few friendly losses as possible, all other considerations being secondary at best. A good in-depth defense premised on bunkers and trenches may provide tactical elasticity, but it clearly identifies operational elasticity as undesirable. There is clear incompatibility here, and in this Baltic case, NATO has politically positioned itself in a way that will require some sort of move away from maneuver defense, at least on a major geographical scale. An orientation toward an operationally static, even if in practice tactically elastic, defense will put emphasis on fires into the Russian rear and deep to attrite Russian forces and damage Russian logistics so that they experience difficulties deploying forces opposite the defensive line itself, let alone directly attacking it. Yet Western political leaders may be squeamish about such attacks — witness their present injunctions against Ukraine’s use of Western weapons against targets in Russia itself. The damage Russia has sustained inside its own borders suggests that the West’s fear of escalation is overblown and, given the combination of regime control over the media and the Russian population’s own considerable apathy, constant scenes of savaged Russian convoys and destroyed Russian transport infrastructure in Russia itself may contribute to turning the Russian population against a hypothetically ongoing Russian attempt to invade the Baltic states. Latvian, Lithuanian, and Estonian purchases of HIMARS rocket launchers and ATACMS (long-range, guided missiles with a range of up to 300 kilometers) demonstrate that the Baltic states are at least serious about having the capability to strike deep. However, in the event of a major Russian invasion, Baltic artillery, and emerging multiple-launch rocket system arsenals — the HIMARS the Baltic states have ordered from the United States — would be unlikely to sustain such interdiction for long. The ultimate hope is that the increasing preparedness of the Baltic states and the wider alliance to fight Russia, among which the construction of the Baltic defense line would be counted, would be sufficient to convince the Kremlin to be deterred. Neither the Baltic states nor the West as a whole has any direct control over the outcome of such a decision. At best, all it can do is present an intimidating picture of negative consequences for Russia to consider. If and when the Baltic defense line is completed, the prospect of denying Russia plausible victory in the Baltic theater in a war against NATO should be stronger and may weigh heavier on the minds of Russian decision-makers. Unfortunately, we can almost never know for sure, as there is no way to know why someone has not done something — deterred, never interested, or is it simply not time yet? The Baltic defensive line is a totally logical response to the particular geostrategic challenges Balts face against Russia, even though it will incentivize ways of fighting against Russians with which, for varying reasons, their Western allies may find themselves tactically, operationally, strategically, or even politically uncomfortable. However, preferred Western alternatives — maneuvering defense and possibly limiting strikes into Russia — would be politically, strategically, operationally, and tactically counterproductive for a NATO that fights against Russia on the eastern flank. The Baltic defensive line should nonetheless contribute to a geostrategic picture of denying the prospect of victory in the Baltic, which will hopefully help induce Russia to choose to be deterred. The views expressed in this article are those of the author alone and do not necessarily reflect the position of the Foreign Policy Research Institute, a non-partisan organization that seeks to publish well-argued, policy-oriented articles on American foreign policy and national security priorities.