Nothing Happens Until Something Moves: Infrastructure Development Priorities on NATO’s Eastern Flank

Over the past decade, NATO’s containment line has steadily shifted eastward, stretching from the Baltic Sea in the north through the Black Sea region and into the Eastern Mediterranean. This repositioning started in 2008, when the Black Sea began to be a conflictual area: Russia invaded Georgia that year, and in 2014 Russia annexed Crimea and then went into a full war with Ukraine beginning in 2022. These events underscored the growing volatility on NATO’s eastern periphery and exposed critical weaknesses in regional infrastructure that continue to hinder military integration and rapid reinforcement.

Despite being a frontline zone, the region remains poorly interconnected: north–south transportation corridors are sparse, with limited highways and outdated railways that fail to support the heavy and coordinated movements required for modern NATO operations. These gaps have been repeatedly highlighted during NATO exercises, where slow transit times, chokepoints, and cross-border delays have revealed the operational cost of underinvestment.

Since the escalation of Russia’s war on Ukraine, the urgency to address these infrastructure shortfalls has only grown. The inability to swiftly move troops and equipment from the Baltic to the Black Sea—or from Greece through Bulgaria and Romania—presents a direct challenge to NATO’s readiness posture. Recognizing these operational vulnerabilities and the strategic importance of enabling swift reinforcement along its eastern flank as well as the need to bolster energy and cyber resilience, NATO used the 2025 Summit as a turning point to align its defense investment framework with the logistical realities of modern warfare.

Therefore, the summit in The Hague marked a major shift in how the Alliance conceptualizes defense spending—not just because Allies are committed to a new 5% of GDP target, but because, for the first time, NATO formally acknowledged that non-military budgets in areas that bolster security (like infrastructure, energy, and cyber resilience) can and should count toward that target. This dual-structure approach allocates 3.5% to traditional defense and up to 1.5% to broader security and infrastructure investments. The summit also marked a notable shift in European posture, with EU institutions and European NATO members signaling that they will be committing more robustly than ever before to funding and developing not only defense capabilities but also the infrastructure and logistical backbone needed for collective defense. 

Policy Build-up and Content 

While this may appear as a policy leap, it is, in fact, the culmination of years of strategic evolution within NATO. Since 2016, NATO has increasingly highlighted the importance of military mobility and civil preparedness, particularly in the underdeveloped infrastructure zones of the eastern flank. The issue gained momentum following the 2016 Warsaw Summit, where NATO first adopted national resilience as a formal benchmark and began focusing on the protection and adaptation of critical civilian infrastructure. Around the same time, the Three Seas Initiative (3SI) was launched by Central and Eastern European countries to develop north–south connectivity—especially road, rail, and energy infrastructure. Notably, this initiative received strong support from the United States, during the first Trump mandate, which saw the effort as a strategic element for deterrence against Russian influence, given also the economic benefits that the integrated infrastructure brings forth.

Against this backdrop, NATO summits from 2018 onward began to recognize the operational implications of inadequate transport and logistics infrastructure in Eastern Europe. The Brussels 2018 Summit, for instance, endorsed NATO–EU cooperation on military mobility, and EU funds were subsequently allocated to upgrade dual-use infrastructure.[1] Yet these investments were never considered part of NATO’s formal 2% spending benchmark. It wasn’t until The Hague Summit in 2025 that the political and strategic consensus matured enough to justify restructuring the spending pledge itself—explicitly separating defense from broader security investments while allowing both to count toward the 5% goal.

This restructured spending framework introduced both a floor and a ceiling: countries must allocate at least 3.5% of GDP to traditional defense spending, while up to 1.5% may be directed toward dual-use or infrastructure-related investments. To qualify under the 1.5% category earmarked for broader security and resilience, infrastructure projects must demonstrably support defense or national security objectives. Acceptable areas include strengthening critical infrastructure like transport routes and power grids, enhancing military mobility corridors, improving cyber and communication networks, bolstering civil preparedness systems, and expanding the defense industrial base. The guiding principle is "dual-use"—investments must serve both civilian functions and military relevance. For instance, upgrading a bridge to handle the weight of tanks or deepening a port to accommodate naval vessels would qualify, whereas routine civilian infrastructure work with no direct security function would not. 

The system ensures that most resources still go to core military needs while giving nations flexibility to address the logistical and resilience challenges essential to modern defense. Each ally must submit detailed annual spending plans showing how funds are split between the two categories. To prevent misuse—such as counting unrelated civilian projects—NATO will conduct a review in 2029 to evaluate the “trajectory and balance” of these expenditures. While the inclusion of infrastructure was a political compromise, it made the 5% target more achievable. The new framework enables governments to mobilize funding from outside their defense ministries—like from transport or interior budgets—and classify relevant projects, such as road and rail improvements along NATO’s eastern flank, as defense-related, provided they serve troop deployment, reinforcement, or strategic mobility goals. 

Who Pays for All This? – Not Just the Member States 

The 5% of GDP defense investment pledge established at the 2025 NATO Summit is ultimately a national obligation: each NATO member must marshal resources equivalent to 5% of its own economy to strengthen collective defense.[2]  However, the investments that count toward this target can come from either purely national initiatives or co-financed projects with NATO and the EU—so long as the member state contributes its own funds to eligible defense-related activities. Most of the dual-use infrastructure spending—such as road, rail, and port improvements for military mobility—will continue to be financed directly through national budgets. If a government allocates funding for a strategic highway upgrade or a new logistics hub that meets military requirements, even if managed by civilian ministries, it can classify that expenditure under the 1.5% category for broader security. NATO has emphasized that allies retain full flexibility in deciding how to structure this spending, allowing them to repurpose existing infrastructure plans, align civil works with defense goals, or increase overall public investment as long as the end result strengthens operational readiness.

In parallel, NATO’s common funding tools, particularly the NATO Security Investment Programme (NSIP), offer mechanisms to support multinational defense infrastructure projects. These include upgrades to critical shared assets like airbases, fuel pipelines, pre-positioned storage, and command facilities across NATO territory. When NATO funds such a project in a member country, that nation’s national contribution to the project (or to NATO’s broader common budget) can be counted toward its defense spending. While the new 5% guideline does not designate a separate carve-out for NATO common-funded projects, it recognizes that these pooled investments ultimately originate from national defense contributions. For this reason, NATO encourages allies to leverage collective initiatives—especially those focused on enhancing logistics infrastructure and rapid reinforcement capacity—to improve interoperability and burden-sharing across the Alliance.

Many NATO members that are also part of the European Union benefit significantly from the EU’s Military Mobility initiatives, particularly under the Connecting Europe Facility (CEF). This program provides up to 50% co-financing for dual-use transport infrastructure projects that meet military requirements—ranging from reinforced bridges and upgraded railway lines to improved port and airport access. While only the national portion of co-funded projects counts toward NATO’s 5% spending target, this setup allows countries to stretch their defense budgets further while aligning with both NATO and EU strategic objectives. In practice, it creates a win–win: NATO gains enhanced military readiness, the EU achieves better regional connectivity, and nations meet multiple obligations through coordinated investment. This cooperative model is especially beneficial for Eastern European allies with substantial infrastructure gaps, offering them a way to accelerate military mobility improvements without shouldering the full financial burden alone.

To fully leverage the cooperative mechanisms available through both NATO and the EU, member states must engage strategically using their negotiation power to align national priorities with broader alliance goals. Accessing EU co-financing for military mobility or shaping NATO’s common funding priorities requires active diplomatic coordination, coalition-building, and long-term planning. Countries that successfully articulate how their infrastructure projects serve collective defense—such as cross-border rail links, Danube improvements bridges, or port expansions—are more likely to secure support and funding. The key ingredient in this process is establishing common interests with neighboring countries and working together to improve interconnectivity. By acting collectively, states can amplify their voice within both institutions, ensure continuity across infrastructure networks, and ultimately turn individual national investments into assets that strengthen the alliance as a whole.

What to Build? Lessons of NATO Exercises for Infrastructure Investment

While national interests in infrastructure development naturally differ across regions and countries—reflecting varied geographies, threat perceptions, and economic capacities—there is a growing body of guidance emerging from past NATO exercises that can help align those interests within the broader goals of the Alliance. These exercises have repeatedly exposed concrete vulnerabilities: on the eastern flank, road and railway networks remain inadequate for rapid troop movement, while in Western Europe, the focus has increasingly shifted to energy infrastructure and cybersecurity resilience.

Although member states are still in the process of defining their national priorities, they are also beginning to identify overlapping needs with neighbors, opportunities for cross-border cooperation, and potential sources of funding—whether national, NATO, or EU. Because NATO conducts large-scale mobility and reinforcement exercises annually, there is now a consistent set of operational lessons pointing to where improvements are most urgently needed. 

Given that the Eastern flank has emerged as the Alliance’s new containment line—stretching from the Baltic Sea to the Black Sea and further toward the Eastern Mediterranean—the following section reviews key exercises that have underscored the persistent North–South interconnectivity problems across this strategically vital corridor.

Estonia

Large NATO drills have tested Estonia’s transportation network. Recent exercises like Hedgehog 2024 and Steadfast Defender validated that improved infrastructure (and Host Nation Support) can support rapid troop movements into Estonia, but also underscored the need for continued upgrades and redundant routes (e.g. using secondary roads or civilian airfields in dispersal scenarios). For example, British Challenger-2 tanks deploying to Estonia highlighted road limits – a tank on a transporter (~80 tons total) exceeds typical road weight limits (40 t) and barely fits under bridge height clearances.[3] Estonia is now upgrading bridges and roads to accommodate allied armor, with ~€100 million (half EU-funded) spent reinforcing key highway sections.[4]

The primary route for moving NATO forces into Estonia is the E67 “Via Baltica” highway, which runs north-south from Latvia to Tallinn. Estonia’s railway network is broad-gauge and connects to Latvia, with key railheads near Tapa (the main NATO training base) and the Port of Paldiski (an offload point for Allied equipment).

Estonia has made military mobility a national priority. Ongoing projects include modernizing Via Baltica and its extensions (aiming for a continuous 2+2 lane highway) and reinforcing dozens of bridges.[5] Under EU and NATO programs, Estonia is investing in dual-use infrastructure like the Rail Baltica railway and improvements at ports/airfields. Notably, EU Military Mobility funds in 2024 are co-financing the Salacgrīva bridge (on the EE/LV border) and other Baltic rail upgrades, which will close bottlenecks on the north–south corridor.[6] These efforts, alongside streamlined border procedures, are enhancing Estonia’s ability to swiftly receive allied reinforcements in a crisis.

Latvia 

Latvia lies in the middle of the Baltic transit corridor. The E67 Via Baltica highway enters from Lithuania, passes through Riga, and continues to Estonia – serving as the backbone for NATO road convoys. Another important route is the east–west E22/A6 road and rail line from the port of Riga toward Daugavpils (and on to Lithuania), which could support lateral movement or an alternate path if Via Baltica were disrupted. Latvia’s rail network (also 1,520 mm gauge) connects to Lithuania and Estonia; a key node is Riga, where a NATO eFP brigade is based (at Ādaži) and equipment can arrive by sea or rail.

As with Estonia, weight limits on Latvian infrastructure have required creative solutions. In NATO moves through Latvia, convoys often need route approval and escort due to road quality and bridge limits. For instance, during Saber Strike and Defender-Europe movements, heavy trucks re-routed to avoid weaker bridges in rural areas. Additionally, differing rail gauges mean that heavy armor from Poland is usually transported by road across the Suwalki Gap instead of by rail,[7] increasing wear on Latvian roads.

Latvia is actively leveraging NATO and EU programs to upgrade infrastructure. Under the EU’s Connecting Europe Facility, of €153 million was granted to Latvia for Rail Baltica construction in 2022 – this will create a high-capacity standard-gauge route through Riga (including a new Daugava rail bridge) for both civilian and military transport. Road projects focus on completing Via Baltica’s missing high-speed segments by 2030 and strengthening alternate routes. The government’s Military Mobility plan (2023) earmarks funds to upgrade 34 km of strategic highways and rebuild critical bridges (like Daugavpils’ Vienības bridge) to accommodate NATO heavy equipment.[8][9] At Riga Port, NATO investment (via the US European Deterrence Initiative) has improved rail yards and piers to handle roll-on/roll-off delivery of armor.[10] These upgrades, combined with exercises integrating civilian rail operators (e.g. PKP Cargo training to load armor), are steadily improving Latvia’s throughput for NATO deployments. 

Lithuania 

Lithuania controls the critical gateway between Poland and the Baltics. The Suwalki Gap – a 65 km land corridor at the LT/PL border – carries Via Baltica (A5 highway) and the planned Rail Baltica line. From the Polish border at Kalvarija, Via Baltica runs north via Kaunas (junction with the east–west A1 motorway from Klaipėda port) and continues to Latvia. Another notable route is the Kaunas–Vilnius–Daugavpils rail line, which allows movement toward Latvia and was used in exercises to reposition forces within the Baltics. Lithuania also has a strategic seaport at Klaipėda, used to land equipment for exercises like BALTOPS, with onward movement by road and rail inland.

Lithuania’s portion of the “Suwalki corridor” has been a focus of NATO contingency planning. Defender-Europe 20 (though curtailed by COVID) and Defender-Europe 22 both tested moving US Army brigades through Poland into Lithuania. These exercises underscored that even peacetime road convoys need careful timing: convoys experienced bottlenecks in Kaunas where city traffic and narrow interchanges caused delays. During Zapad 2021 (a Russian exercise simulating an attack on Suwałki), NATO observers noted the urgency of mobility – prompting Lithuania to accelerate projects in that corridor. Overall, exercises have highlighted that timely reinforcement of Lithuania hinges on rapidly surging troops through one narrow corridor, driving home the point that every road and bridge there must be in top shape.

Lithuania has undertaken major upgrades with EU and NATO help. Via Baltica Expansion: The country, with €60 million EU co-funding, is reconstructing the Via Baltica (A5) from Marijampolė to the Polish border as a four-lane highway, eliminating the last two-lane stretch. This upgrade (to finish by mid-2020s) will significantly boost road throughput for military convoys. Lithuania is also building its segment of the new standard-gauge Rail Baltica line. By 2023, the line from Poland to Kaunas was operational for limited use; further extension toward Latvia is ongoing.[11] Importantly, a military/civilian rail loading facility at Palemonas (Kaunas) received €13 million EU funding – allowing tanks and heavy equipment to transfer between trains and road or be staged. Lithuania is also upgrading the Vilnius–Augustów secondary road (via Lazdijai) to serve as an alternative military route, including reinforcing eight bridges along it.[12] Under NATO NSIP, improvements at the Pabradė training area rail spur and enhancements to Klaipėda Port facilities have been made to support rapid unloading of naval transports. Together, these efforts address the very “weakest link” of NATO’s East – by expanding capacity and resilience in the Suwałki Corridor.

Poland

As NATO’s frontline hub, Poland hosts multiple corridors used in recent exercises. The chief west-east artery is the A2 motorway (and parallel E20 rail line) from Germany to Poznań–Warsaw and onward towards Belarus – this was used heavily in Defender-Europe 20/22 to flow US forces from German ports across Poland.[13] For north-south movement, the Via Baltica (S61) expressway runs from Warsaw north to the Lithuanian border, enabling reinforcement of the Baltic states. Poland’s rail network is dense; a key line for NATO is the Rail Corridor from Germany through Poznań to Łódź–Warsaw (part of EU TEN-T Corridor II). Another important route is the A4 motorway (and rail links) in southern Poland, used to shift US units toward the Black Sea region via Hungary/Romania (as seen in Defender-Europe 21).

Poland has modernized rapidly, but large-scale deployments exposed friction points. A prominent example: during Defender-Europe 20, Polish authorities noted that bureaucratic procedures (permits for oversized loads, hazardous materials, etc.) initially caused delays – lessons learned led to Poland streamlining these via special laws in 2020. Physical infrastructure held up generally well, yet there were instances of convoys detouring to avoid weak bridges on secondary roads. The US Army also practiced wet-gap crossings in Poland (e.g. bridging the Vistula during Defender-Europe 22) to simulate what happens if fixed bridges are destroyed. These wet-gap exercises highlighted that despite many bridges, the Vistula and other rivers remain obstacles – NATO engineers would need to bridge them under fire if necessary. Another issue has been rail capacity: while Poland’s railroads are extensive, civilian traffic can congest key lines. In exercises, Poland had to prioritize military trains and sometimes shift civilian freight schedules to clear the tracks. This demonstrated the need for the new Joint Support and Enabling Command (JSEC) in Germany to coordinate such movements across borders.

Poland, Germany, and the Netherlands in January 2024 signed a Military Transport Corridor agreement to create a “fast lane” from North Sea ports to Poland.[14] This model corridor (a kind of “military Schengen”) streamlines customs, safety inspections, and permits along the route, cutting transit time. In physical terms, Poland has continued expanding the A2 motorway eastward and upgrading rail lines (the Warszawa–Białystok line is being improved as part of Rail Baltica prep). Under NATO’s NSIP and the US European Deterrence Initiative, Poland has built or improved numerous infrastructure nodes: e.g. a new Intermediate Staging Base and rail spur at Pstrąże, upgrades to the Drawsko Pomorskie railhead, and expanded fuel depots for supporting NATO armor. Bridges are being reinforced nationwide – by 2025, Poland reported 170 bridges upgraded to military load class MLC70+ standard. Finally, Poland’s participation in EU PESCO Military Mobility ensures it adapts its laws and shares best practices on things like convoy procedures and dangerous goods transport, further smoothing the way for rapid NATO deployments.[15]

Poland has invested heavily in dual-use infrastructure. Under the EU’s 2021 Military Mobility call, Poland received funds to upgrade A2 motorway bridges to NATO standards (now completed, enabling heavy tank transport). Poland is electrifying and double-tracking the Rail Baltica route within its borders – a new line from Ełk to the Lithuanian border is a “greenfield” project for 250 km/h trains (with military-spec loading). This will eliminate the slow single-track by 2026. Additionally, Poland is expanding railhead facilities in northeast Poland so that multiple battalions can unload simultaneously during a reinforcement surge. New infrastructure like fuel depots and staging areas have been built near Suwałki and Białystok to support transiting forces. On the road side, the Via Carpatia initiative (an international highway corridor) is progressing – for Poland this includes the S19 expressway down to Slovakia, augmenting north-south military mobility. Finally, Poland and Lithuania are jointly upgrading the Vilnius–Augustów road that connects with Poland’s DK8 route, providing an alternate military road parallel to Via Baltica. Through these efforts, Poland is seeking to fortify itself as the lynchpin of NATO’s reinforcement routes to both the Baltic and Black Sea regions.

Hungary

Hungary’s central location makes it a transit hub for NATO moving between Western Europe and the Eastern flank, providing transit corridors to Romania and Slovakia. From Austria/Germany into Hungary, the M1 motorway (Vienna–Budapest) and parallel railway carry incoming forces. Heading toward Romania, the M43 motorway (Szeged–Nădlac) links to Romania’s A1, forming a continuous high-speed road from central Europe into western Romania – this was the route used by US convoys for exercises like Saber Guardian. Another developing route is the M4 motorway eastward from Budapest to Oradea (RO border), which when complete (by 2026) will offer a second highway into northwestern Romania.[16] Northward, Hungary’s M30 motorway and connected roads lead to Slovakia (toward Košice) – part of the Via Carpatia north-south corridor that could facilitate moving troops between the Black Sea region and Poland via Hungary/Slovakia. Key rail lines include the Budapest–Curtici (RO) rail corridor (electrified double-track) feeding into Romania’s rail network, and the Budapest–Čierna nad Tisou (SK/UA) broad-gauge line (for Ukraine aid, primarily). Hungary’s air and logistics hub at Papa Air Base (with its C-17 fleet) also plugs into these surface corridors for onward movement.

Hungary’s highways are generally well-developed; however, the sheer volume of traffic in a major NATO deployment can strain even modern roads. On rail, Hungary’s network is compatible with Western European standards (standard gauge, 25 kV AC electrification on mainlines), so it serves as a smooth conduit. But capacity on the single main line to Romania (via Curtici) is finite. During Defender-Europe movements, scheduling conflicts with civilian freight occurred, suggesting the need for passing loops and station upgrades. Indeed, Hungary launched a project to adapt key rail stations in western Hungary for 740 m military trains to ease flow. Another challenge: bridging between Hungary and Slovakia/Romania. While road bridges at borders are modern (e.g. Mórahalom–Nădlac highway bridge), rail bridge infrastructure is older. The single-track rail bridge at Komárom (HU) to Komárno (SK), for example, could be a chokepoint if large forces were moving north-south by train. Additionally, Hungary’s internal Danube bridges (e.g. between Buda and Pest, or at Szeged over Tisza) must handle heavy military convoys: a nationwide highway audit in 2023–25 is reinforcing dozens of bridges as needed.[17]

Hungary conducted Adaptive Hussars 2023, its largest exercise in 30 years, which notably practiced nationwide military movements and civil-military coordination. This exercise, observed by NATO’s LANDCOM, tested Hungary’s ability to receive and forward deploy another NATO battlegroup on its soil. One lesson was the complexity of coordinating multi-modal logistics – for instance, a Dutch company’s tanks arrived by rail from Germany to western Hungary, then road-marched to an eastern training area. This revealed excellent rail infrastructure in the west (thanks to investment) but a need for more railheads in the east. Allied units transiting Hungary to Romania during Defender-Europe 21 reported generally smooth movement along M43, aided by Hungary’s proactive traffic management. However, heavy rainfall at the time exposed that a section of older road on the approach to the border flooded, causing a reroute – underscoring the need for resilient infrastructure and alternate routes. When Hungarian forces deployed to exercises in Slovakia, it often involved moving through one main highway (M15 to Bratislava) – highlighting that for larger operations, more crossing points would be useful. The importance of Hungary’s role was summed up by NATO officials: reinforcing the eastern flank could require moving a brigade through Hungary to Romania within 2–3 days, so everything from rail schedules to bridge classifications must be in order ahead of time.

Hungary has been upgrading both road and rail for dual civilian-military use, often with EU funding. The country secured EU funds to complete the M4 motorway to Romania,[18] closing the gap by 2024–2025. It also plans a new M49 motorway toward Satu Mare (RO) by 2026,[19] creating a future highway link to northern Romania. These will supplement the busy M43/Nădlac route, distributing traffic. In 2023 Hungary began its largest expressway upgrade program, resurfacing and strengthening 43% of main roads by 2025 (hungarytoday.hu)[20] – many along NATO routes. On the rail side, under the EU’s military mobility envelope, a project (21-HU-TM-WestHun) is adapting western Hungary’s rail hubs for dual-use. This includes lengthening tracks for 740 m trains (NATO standard) and improving loading facilities at Győr and Szolnok. Hungary is also participating in the Network of Logistic Hubs PESCO project – potentially hosting a regional logistics hub for NATO/EU. As part of this, a new military warehouse complex is planned near Debrecen (eastern Hungary), which sits on the road/rail route to Romania. Finally, Hungary’s NATO Force Integration Unit (NFIU) in Székesfehérvár is improving coordination for transit; it serves as a 24/7 point of contact to expedite any reinforcement movement across Hungary. Together, these efforts ensure that Hungary can fulfill its crucial role as a fast and efficient transit corridor for NATO, linking the Alliance’s heartland to its Eastern frontier.

Romania

Romania is a key point for NATO’s southeastern flank exercises. One major corridor is the Pan-European Transport Corridor IV, which enters from Hungary at Nadlac and follows the A1 motorway (and parallel rail line) through Arad–Timișoara–Sibiu, across the Carpathian Mountains to Bucharest, and onward to the Black Sea (Constanța). This route was used by allied forces in Defender-Europe 21 and Saber Guardian to move troops from Central Europe into Romania. Another vital route is the Danube crossing from Bulgaria: the DN5/E85 highway from Ruse (BG) to Bucharest (RO) over the Danube Bridge (Giurgiu-Ruse) has carried US and NATO convoys coming from Greece via Bulgaria. Additionally, Romania’s rail network has key nodes at the port of Constanța and the rail border crossing at Curtici (from Hungary). The Constanța–Bucharest–Brașov rail line and onward to Hungary is essentially the rail equivalent of Corridor IV.

NATO exercises in Romania have repeatedly spotlighted infrastructure shortfalls. The Carpathian passes are a single point of failure: if the rail tunnels or road passes there are knocked out, reinforcement from Western Europe would be forced into lengthy detours (or reliant on air/sea lift). During Saber Guardian 2019, US Army units had to use Romanian Railways (CFR) to haul tanks because roads couldn’t handle them – a solution, but CFR’s unreliable engines and 19th-century track caused frequent breakdowns and delays (noted in exercise after-action reports). Moreover, Romania’s rail network suffers from underinvestment: retired bridges and speed-restricted tracks abound, meaning military trains can take days to traverse the country. While railroads are to be avoided, there is a limited number of highways that may be used and they also don’t help an easy passage of the Carpathians at the moment. The Danube crossings present a strategic vulnerability – NATO logistics planners consider the Danube a natural barrier; bridging units would be necessary if the fixed bridges were lost. Moreover, the Danube could also be developed into a functional corridor linking Germany to the Black Sea – especially since it is currently underdeveloped.

Recognizing these issues, Romania and its neighbors have initiated major upgrades. Romania is investing in finishing the A1/A3 motorways over the Carpathians (the Sibiu–Pitești highway segment, under construction with EU funds, will greatly speed road convoys). Rail modernization is ongoing on Corridor IV (the Brașov–Sibiu–Curtici line is being upgraded for 160 km/h, though work is slow). In 2023, the EU agreed to fund a feasibility study for a third bridge over the Danube (at Silistra–Călărași), aimed at easing north-south military mobility. On the sidelines of the Washington Summit which has recognized yet again the poor interconnection in Southern Europe, together with Bulgaria and Greece, Romania signed a Letter of Intent in July 2024 to establish a “Harmonized Military Mobility Corridor” from the Aegean to the Black Sea – connecting Thessaloniki, Alexandroupoli, Varna, and Constanța – with the goal of fluent border crossings and infrastructure upgrades along this route. The discussions included the construction of another bridge on the Danube as well as a motorway connecting Bucharest to Giurgiu (A5) – but the feasibility study was only awarded in 2025 and the A5 doesn’t seem to be a priority anymore. The NATO’s Security Investment Programme (NSIP) has also poured resources into Romania: examples include expanding fuel pipelines and storage (the NATO pipeline network in Romania has been enhanced for military use), improving airbases (e.g. Câmpia Turzii and Mihail Kogălniceanu), and constructing a large NATO logistics hub near Constanța (sometimes cited as “the biggest NATO base in Europe” under construction). While progress is slower than desired, these efforts – along with regulatory tweaks like Romania’s new laws allowing quicker movement permissions – are gradually mitigating the vulnerabilities that exercises have laid bare.

Bulgaria 

Bulgaria is the crossroads for the southern approach to Romania. The primary military corridor runs north–south from the Aegean Sea, through Bulgaria, to the Danube. This includes the Makaza–Kapitan Petko Voivoda border crossing from Greece (for traffic from the Greek port of Alexandroupoli or Thessaloniki), linking to Bulgaria’s Maritsa motorway (A4) and onward via E85 highway through Veliko Tărnovo to the Danube Bridge at Ruse. Additionally, the Thrace highway (A1 “Trakia”) from Sofia to Burgas, and the Black Sea coastal road to Varna, are relevant if equipment arrives at Bulgarian Black Sea ports. For rail, the Svilengrad–Plovdiv–Ruse rail line is crucial: it connects the Greek border (at Svilengrad/Ormenio) to Ruse and thus into Romania. Another rail route of note is from Burgas port up to Ruse. Bulgaria also hosts the Novo Selo Training Area near the Aegean route, which US forces use (requiring local road improvements to handle armor).

Bulgaria’s role as a transit country means that any delays on its territory can ripple outward. Prior to improvements, border crossing times from Greece to Bulgaria could be lengthy – e.g. in Defender-Europe 21, the US noted the need for quicker processing at Kulata checkpoint. Bulgaria has since coordinated with Greece to pre-clear convoys. The Danube bottleneck remains the top concern: during exercises, convoys have queued at Ruse bridge and rail freight had to be scheduled carefully to avoid stranding military trains. Bulgarian railways, similar to Romania’s, are outdated in parts – an EU Parliament report identified 500+ military mobility “hot spots” in Europe, many in BG/RO (like weight-limited bridges and slow border procedures). Bulgarian and US forces have mitigated some issues by using multimodal solutions – for example, sending heavy cargo by ferry across the Black Sea to Constanța to avoid the Danube bridge, or using C-17 airlift into Plovdiv when roads were too slow. Nonetheless, the terrain (mountains and the Danube) and infrastructure (limited highways, single Danube crossing) continue to challenge large-scale movements.

Bulgaria, Greece, and Romania have launched joint initiatives to strengthen this corridor. In late 2023, Bulgaria and Greece agreed to “build up military transport capacity” by improving the rail link from Alexandroupoli through Svilengrad. Greece is financing a €1 billion project to reactivate and dual-track the Alexandroupoli–Svilengrad rail line by 2028, which will greatly enhance throughput into Bulgaria. In parallel, the long-discussed “Sea2Sea” project is back on the table: this would connect Greece’s Aegean ports (Alexandroupoli, Kavala, Thessaloniki) by modern rail to Bulgaria’s ports (Burgas, Varna) and to Ruse on the Danube. Sea2Sea is envisioned as both an economic and military mobility route, providing an alternative to the Turkish Straits and a more direct path for US equipment into the Black Sea region. Moreover, as noted, a new Danube bridge at Ruse is being fast-tracked with EU support – it’s considered part of a key EU/NATO corridor and will tie into a future high-speed rail line from Greece up to Romania. Domestically, Bulgaria’s Integrated Transport Strategy (2030) includes four new Danube bridges and completion of the Hemus and Black Sea highways.[21] While these projects are in early stages, NATO has already tested temporary solutions (like deploying tactical bridging units in Bulgaria) to ensure that, even today, forces can be supported. Every successive exercise – from Thracian Viper to Steadfast Defender 24 – has shown incremental improvements in Bulgaria’s ability to host and transit NATO forces, validating the ongoing infrastructure investments.

Greece 

Greece serves as the southern entry point for NATO’s Eastern flank via its ports and road network. The standout is Alexandroupoli Port, on the Aegean, which since 2019 has become a major offload hub for US Army equipment bound for Eastern Europe. From Alexandroupoli, the E85 highway runs north to the Bulgarian border at Kipoi/Ormenio, connecting onward to Bulgaria’s E85/DN5 route to Romania. Similarly, a rail line from Alexandroupoli heads north to Svilengrad (BG). Another route is via Thessaloniki, Greece’s largest northern port: from Thessaloniki, both road (A25 motorway) and rail go north through Promachonas to Sofia (BG), feeding into the same Danube corridor eventually. These routes were utilized in Defender-Europe 21, when US forces landed a large amount of hardware in Alexandroupoli and moved it into Bulgaria and Romania.

Greece’s main challenge was not so much its internal infrastructure but rather coordination and capacity at the Alexandroupoli node. When large volumes of US equipment arrived for Defender-Europe 21, it tested the port’s limits – yet the operation was successful, earning praise that Alexandroupoli had become “vital for the flow of personnel and equipment” to NATO’s eastern flank. Still, exercises uncovered issues: limited railcars for onward movement (Greece had to borrow flatbed rail wagons from other European railways to move armored vehicles north). Also, the Alexandroupoli rail line’s low speed meant many units simply convoyed by road through Bulgaria, which is efficient but puts more strain on the roads. Another consideration was diplomatic: large US movements from Greece drew concern from Turkey and Russia, though not a physical obstacle, it underscores the strategic sensitivity of this corridor. In terms of pure infrastructure: the port of Alexandroupoli previously had limited staging area – the US Army leased additional land to store equipment during surge operations. On the Thessaloniki side, while that port is bigger, the route into Bulgaria from there was not used as heavily in 2020–25, partly to avoid the longer distance.

Greece has actively embraced its role as a strategic logistics hub. The port of Alexandroupoli saw significant investment: dredging (as noted), new cranes, and an expansion plan to handle more ships simultaneously. The US–Greece updated Mutual Defense Cooperation Agreement (2021) specifically references Alexandroupoli for joint use, and a portion of US ERI (European Reinforcement Initiative) funds have gone into port improvements and a rail spur connection. On the rail front, Greece’s national railway and Bulgaria’s signed agreements to upgrade the Alexandroupoli–Burgas–Varna “Sea2Sea” rail corridor, backed by EU military mobility funds. By late 2024, Greece, Bulgaria, and Romania are holding implementation meetings for the Harmonized Military Mobility Corridor connecting their territories– this will address remaining bureaucratic hurdles and coordinate infrastructure upgrades so that, for example, a NATO convoy can drive from Alexandroupoli to Constanța with minimal stops. In addition, Greece’s armed forces and infrastructure ministry have been mapping out all critical roads and bridges in the north for reinforcement; one Greek initiative proposed launching through-freight trains from Greece to Romania and even Poland for military use.[22] Finally, Greece’s inclusion in NATO’s broader mobility planning (through exercises and table-top drills) has ensured that the lessons from 2020–2025 are acted upon. The rapid throughput achieved via Alexandroupoli in support of Ukraine and NATO (an estimated 60% of US forces for NATO’s eastern flank transited there by mid-2023) has solidified Greece’s value, prompting continued investment so these corridors remain ready and even surge-capable for future Allied deployments. This also explains Greece inclusion in the 3 Seas Initiative platform, considering Athens’ interest to participate in growing the investment in dual-use infrastructure.

Conclusion

Based on the research and patterns observed across NATO exercises on the Eastern flank from 2020 to 2025—including Defender-Europe, Saber Strike, Saber Guardian, Steadfast Defender, and Adaptive Hussars—there are several potential investment priorities, repeatedly highlighted by real-world movement challenges.

Bridge reinforcement and load upgrades

NATO exercises over the past five years have repeatedly exposed the vulnerability of aging road and rail bridges across the Eastern flank. In countries like Latvia, Romania, Hungary, and Poland, bridge weight limits have forced convoys to reroute, delay, or restrict vehicle loads. Exercises such as Defender-Europe and Saber Guardian revealed that critical military assets like Abrams tanks and armored bridging vehicles could not cross several rural or even arterial bridges without additional reinforcement or weight waivers. In Hungary, 18 priority road bridges are undergoing reinforcement to meet NATO heavy-load standards, while Latvia is prioritizing major crossings like Daugavpils’ Vienības Bridge and the Danube bridges (improving the existing and building new ones) become a priority for Bulgaria and Romania.

Investments in bridge modernization are essential not just to support military mobility but to create resilience in the broader transport network. NATO’s emphasis on interoperability means that all transit routes must be certified to support the heaviest Alliance equipment. Without this, any damage or sabotage to a mainline route could effectively cut off entire flanks from reinforcement. Bridge upgrades are thus a cornerstone of military mobility funding under EU and PESCO initiatives and will remain critical over the next decade. 

Suwałki gap corridor reinforcement (road and rail)

The Suwałki Gap, a narrow 60–80 km corridor between Poland and Lithuania flanked by Kaliningrad and Belarus, remains NATO’s most geopolitically sensitive land connection to the Baltic states. Exercises like Steadfast Defender and Saber Strike have simulated its blockage and tested reinforcement options. These drills highlighted vulnerabilities not only to kinetic attack but to basic infrastructure overload. Poland’s S61 expressway and complementary rail lines were frequently used in simulations, but some stretches lacked full military load certification or presented logistical chokepoints under surge traffic.

In response, major investments are being directed toward completing Via Baltica (S61/A5) and fast-tracking Rail Baltica, a standard-gauge, high-speed railway through Lithuania, Latvia, and Estonia. These routes not only improve speed and load capacity but also offer NATO redundancy and strategic depth. Still, the corridor’s security depends not only on connectivity but on rapid deployability—underscoring the need for hardened roads, backup crossings, and alternative east-west lines that would keep supply and troop flows open even under attack.

Rail gauge and throughput bottlenecks

Exercises have shown that rail remains the backbone of strategic deployments across Europe, but Eastern flank countries still face legacy infrastructure constraints. The gauge mismatch between Poland (standard gauge) and the Baltics (broad gauge) creates friction for northbound deployments. Additionally, limited flatcar availability, narrow sidings, and short platform lengths often mean that NATO-standard 740 m military trains must be broken down or routed inefficiently. For instance, during Defender-Europe 2021, delays in Lithuania were traced directly to gauge transfer issues and sidings not designed for military cargo.

Efforts like Rail Baltica (standard gauge to Tallinn) and station modernizations in Hungary (e.g., Békéscsaba, Mezőtúr) are addressing these issues. Double-tracking key segments—like Hungary’s Békéscsaba–Lőkösháza line to Romania—is a priority, as is upgrading transshipment hubs such as Kaunas Palemonas and Felsőzsolca. These upgrades will not only ease military congestion but offer long-term benefits to freight corridors under the EU’s TEN-T initiative.

Danube crossing capacity and the DN5/A5 Bottleneck

Romania and Bulgaria rely heavily on just two permanent road/rail bridges across the Danube—the Giurgiu–Ruse and Vidin–Calafat crossings. During exercises like Saber Guardian 2021, convoys experienced long delays at Giurgiu due to narrow bridge lanes, summer heat restrictions, and limited staging space. The conclusions of Steadfast Defender 2024 and Dacian Spring 2025 highlight persistent vulnerabilities in DN5’s capacity and quality, which remain a stumbling block for military mobility along the stretch leading to the Danube crossing. The current road corridor (DN5) linking Bucharest to the Giurgiu border is a national road without full highway standards, creating a serious chokepoint. Military convoys must navigate roundabouts, lack of shoulders, and non-separated traffic as well as residential areas, causing safety and scheduling concerns.

To address this, Romania has proposed the A5 motorway, a 51 km high-speed bypass designed to relieve DN5 and connect directly to Bulgaria's planned Ruse–Veliko Tarnovo motorway. However, A5 remains in the feasibility phase and has not been prioritized for near-term construction. Meanwhile, a second Danube bridge at Giurgiu–Ruse is under study, co-funded by the EU, but still years from materialization. Without these upgrades, the southeastern flank remains dependent on overburdened infrastructure that constrains both rapid deployment and long-term deterrence.

Port capacity and rail integration

As NATO diversifies its logistics footprint beyond the Suwałki Gap, seaports like Alexandroupoli (Greece), Constanța (Romania), Riga, Klaipėda, and Gdynia (Poland) have become vital entry points. However, exercises revealed gaps in rail access, heavy-lift capability, and staging area size at several of these ports. For instance, while US armor was successfully offloaded at Alexandroupoli in Defender-Europe 2021, delays occurred in onward movement due to underdeveloped rail links and insufficient platform strength.

Investments at Alexandroupoli and Constanța—funded by the US European Deterrence Initiative and EU CEF—are improving Roll–On/Roll–Off capabilities, rail sidings, and nearby highways. In Latvia and Estonia, ports are expanding flatcar capacity and building hardened piers. The priority is to create integrated, dual-use port nodes capable of moving full brigade-sized deployments within days, with redundancy for simultaneous commercial use.

Redundant and secondary routes

Exercises have made it clear that NATO must avoid over-reliance on a handful of key corridors. In scenarios tested in Anakonda 2020 and Steadfast Defender 2023, attacks or cyber disruptions on single motorways or rail lines paralyzed force movement. Nations like Poland, Romania, and the Baltics are therefore mapping and upgrading secondary roads and local rail lines that can serve as alternates during crises.

These efforts include converting civilian roads to military-grade standards, constructing modular bridges, and pre-positioning engineering assets for emergency repairs. For example, Romania’s work on the A7 corridor and Moldova border links offers alternate access to northeastern regions, while Lithuania is upgrading east–west roads from Kaunas to Alytus. Redundancy is no longer a luxury—it’s a requirement for credible deterrence.

While many of the infrastructure upgrades discussed—bridges, highways, rail lines, and port enhancements—are still under national evaluation or in early planning stages, NATO exercises over the past five years have provided concrete, real-world evidence of their strategic value. These drills do more than test military readiness; they reveal the logistical bottlenecks and vulnerabilities that national planners might otherwise overlook. In doing so, they offer a clear platform for identifying dual-use infrastructure investments that serve both defense and civilian purposes.

The opportunity is significant. Projects like Rail Baltica, the A5 motorway, upgraded Danube crossings, and modernized ports not only strengthen NATO’s deterrence posture and response time—they also enhance national resilience, reduce supply chain vulnerabilities, and contribute to long-term economic growth. Investing in infrastructure that meets military requirements while improving trade, mobility, and connectivity is a strategic win-win.

[1] North Atlantic Treaty Organization (NATO), The Secretary General’s Annual Report 2018 (Brussels: NATO, March 15, 2019), https://www.nato.int/nato_static_fl2014/assets/pdf/pdf_publications/20190315_sgar2018-en.pdf.

[2] North Atlantic Treaty Organization (NATO), The Hague Summit Declaration, issued by the NATO Heads of State and Government participating in the meeting of the North Atlantic Council in The Hague, June 25, 2025, https://www.nato.int/cps/en/natohq/official_texts_236705.htm.

[3] ERR News, “Estonia to Upgrade Roads, Bridges to Bear Weight of Allied Armor,” ERR, July 16, 2023, https://news.err.ee/1609418056/estonia-to-upgrade-roads-bridges-to-bear-weight-of-allied-armor.

[4] Ibid.

[5] ERR News, “Estonia to Upgrade Roads.”

[6] State Security Service of Latvia, “Call for Proposals in the Field of Military Mobility: Funding of 788 Million Euros Approved for Latvian Transport Sector Projects,” SAM.gov.lv, accessed August 3, 2025, https://www.sam.gov.lv/en/article/call-proposals-field-military-mobility-funding-788-million-euros-approved-latvian-transport-sector-projects.

[7] RailFreight.com, “This Is All You Need to Know about Military Mobility,” RailFreight, May 6, 2025, https://www.railfreight.com/specials/2025/05/06/this-is-all-you-need-to-know-about-military-mobility/?gdpr=accept.

[8] Ministry of Defence of the Republic of Latvia, “Eastern Border Counter-Mobility Plan Approved in Latvia: EUR 303 Million to Be Invested in Strengthening Security,” Ministry of Defence, June 25, 2024, https://www.mod.gov.lv/en/news/eastern-border-counter-mobility-plan-approved-latvia-eur-303-million-be-invested-strengthening.

[9] Latvian Public Broadcasting, “Plan Pushes Disaster Centers, Military Bases, Anti-Mobility Depots for Eastern Latvia,” Public Broadcasting of Latvia, November 6, 2024, https://eng.lsm.lv/article/society/defense/06.11.2024-plan-pushes-disaster-centers-military-bases-anti-mobility-depots-for-eastern-latvia.a575382/.

[10] Ministry of Defense of Latvia, “Call for Proposals in the Field of Military Mobility.”

[11] Linas Jegelevicius, “The Baltics Look to Strengthen NATO’s Weakest Link,” The Parliament Magazine, March 22, 2024, https://www.theparliamentmagazine.eu/news/article/the-baltics-look-to-strengthen-natos-weakest-link.

[12] LRT English, “Lithuania to Upgrade Militarily Significant Vilnius–Augustow Road by Mid-2028,” LRT, July 24, 2024, https://www.lrt.lt/en/news-in-english/19/2502697/lithuania-to-upgrade-militarily-significant-vilnius-augustow-road-by-mid-2028.

[13] Sabine Siebold, “Three NATO Allies Sign Deal to Speed up Military Deployments on Eastern Flank,” Reuters, January 30, 2024, https://www.reuters.com/world/europe/three-nato-allies-sign-deal-speed-up-military-deployments-eastern-flank-2024-01-30/.

[14] Siebold, “Three NATO Allies Sign Deal.”

[15] JAPCC, “Supporting NATO Deterrence.”

[16] Hungary Today, “Motorway Linking Hungary and Romania to Be Completed in 2026,” Hungary Today, accessed August 3, 2025, https://hungarytoday.hu/motorway-linking-hungary-and-romania-to-be-completed-in-2026/#:~:text=2026%20hungarytoday,of%20Construction%20and%20Transport.

[17] Hungary Today, “Renewal of Expressway Road Surfaces in Full Swing,” Hungary Today, accessed August 3, 2025, https://hungarytoday.hu/renewal-of-expressway-road-surfaces-in-full-swing/#:~:text=Renewal%20of%20Expressway%20Road%20Surfaces,kilometers%20of%20main%20roads.

[18] Global Highways, “EU Loan for Hungary’s M4 Budapest–Romanian Border Road Link,” Global Highways, accessed August 3, 2025, https://www.globalhighways.com/wh8/news/eu-loan-hungarys-m4-budapest-romanian-border#:~:text=border%20www,Hungary%20with%20the%20Romanian%20border.

[19] Hungary Today, “Motorway Linking Hungary and Romania.”

[20] Hungary Today, “Renewal of Expressway Road Surfaces.”

[21] Friendship Bridge, “History of the Bridges between Bulgaria and Romania in the 21st Century,” August 22, 2024, https://friendshipbridge.eu/2024/08/22/history-bridges-bg-ro-21st-century-en/#:~:text=The%20third%20Bulgarian,But%20disputes%20between.

[22] Guillaume Lasconjarias and Thibault Fouillet, “The Port of Alexandroupolis: A Strategic and Geopolitical Assessment,” Fondation pour la Recherche Stratégique, March 14, 2024, https://www.frstrategie.org/en/publications/notes/port-alexandroupolis-strategic-and-geopolitical-assessment-2024#:~:text=the%20EU%20is%20interpreted%20by,corridor%E2%80%9D%2C%20Kathimerini%2C%2014%20March%202024.