Baltic-Polish Military Border Fortifications Echo Pre-War Defenses Destroyed by Stalin and Hitler

Although Poland’s 1939 defense plan (“Plan West”) prioritized the German threat, the army also maintained fortifications on the long eastern frontier with the USSR. Notably, the Sarny Fortified Area in northeastern Volhynia (near Sarny, now in Ukraine) was a line of bunkers and trenches along the Sluch River, built when Polish strategists considered the Soviet Union the main threat.*

Construction at Sarny began in 1936 and was slated for completion in 1940, with a total planned length of 170 km and 358 concrete combat bunkers in up to five defensive belts. These bunkers were manned by the Border Defense Corps (KOP) and were well-equipped (each garrison of 30 soldiers had machine guns and 75 mm guns)​.

By September 1939, much of the Sarny line was in place (albeit not fully armed) and border defense units there later resisted the Soviet invasion on 17 September 1939. Similarly, older Russian fortresses inherited by Poland – such as the Modlin Fortress (north of Warsaw), Osowiec Fortress (on the Biebrza, used as a strongpoint anchoring the Narew line), Brześć/Brest Fortress, and Przemyśl – were integrated into defense plans as nodal strongholds. 

These sites had thick masonry/concrete walls and moats, and although built in the 19th century, they were garrisoned in 1939 as rallying points or to guard river crossings. For example, Modlin Fortress served as a fallback defensive citadel for the Modlin Army and withstood a siege until late September 1939. Brest Fortress likewise was defended against the Germans for several days in 1939 (before capitulating and later being handed to the Soviets).

Estonia’s land border with the Soviet Union was split by Lake Peipus (Peipsi) into two sectors – the northern Narva front and the southern Petseri front – with the lake itself forming a passive barrier in between. Estonian defense planners identified the narrow corridor around Narva (between Lake Peipus and the Gulf of Finland) as a likely Soviet invasion route and thus a priority for fortification. In 1939, work began on a line of permanent border fortifications along the Narva River and further east. 

The engineering plans called for a series of 748 reinforced-concrete installations (bunkers, observation posts, shelters), including 222 weapon emplacements (machine-gun and artillery caponiers)​.

Likewise, in the Petseri county (bordering Soviet Pskov), forts were planned to defend key access routes and the approaches to south Estonia. However, progress was slow – major construction only really kicked off in 1939, and by the time WWII began, the program was still in its infancy.

The interwar Latvian government had limited fortification efforts; Latvian defense strategy leaned toward mobile defense and alliances rather than extensive permanent works. By 1939, Latvia had not constructed any major system of modern border fortifications – a decision influenced by threat perception and geography.

Despite the lack of fixed defenses on the USSR border, Latvia did have natural barriers and some contingency plans. The broad Daugava (Dvina) River bisects Latvia east-to-west, flowing through Daugavpils and Riga, and would have been a logical defensive line. In a crisis, the Latvian Army intended to fall back and use the Daugava as a shield for central Latvia and Riga.

Throughout the interwar period, Lithuania’s primary antagonist was Poland (due to the conflict over Vilnius), but by the late 1930s Nazi Germany had emerged as the greater threat, especially after the annexation of Klaipėda (Memel) in March 1939. 

Lithuania was in the difficult position of having lost its capital (Vilnius) to Poland and its major port (Klaipėda) to Germany just before WWII – which left the nation increasingly vulnerable. In terms of fortifications, Lithuania did not undertake a Maginot-like project; instead, its defensive preparations centered on using natural terrain (rivers, lakes) as defensive lines, and developing obstacles and a militia-based resistance plan. Some local fortifications existed, but by 1939 Lithuania’s defensive system was largely unfinished and untested.

On the eve of World War II, the defensive lines of Poland and the Baltic states ranged from concrete fortress networks to essentially unfortified borders, illustrating how each nation balanced its geography, threats, and resources.

Estonia had begun fortifying its narrow land border and had a formidable coastal artillery defense, yet its land bunkers were unfinished when the Soviet tide arrived. Latvia, lacking natural choke-points and courted by both powers, largely forewent fixed defenses, leaving it exposed. Lithuania, caught between aggressive neighbors, relied on rivers and improvised obstacles rather than forts, and its strategy was untested before Soviet occupation.

Nevertheless, if Baltic nations had not been occupied and Poland was not subjected to communist terror, we would today be discussing modernization and enhancement of the existing Baltic-Polish defensive infrastructure rather than building it anew. Defensive barriers—which would be swiftly expanded and mined if the imminent threat of war arose — are simply a logical component of military defense for countries neighboring an unpredictable and aggressive major power.

Western media outlets (Baltic and Polish media increasingly less so) have grown accustomed to portraying Baltic and broader NATO military reinforcement measures as sensational developments. This isn't necessarily the media’s fault — NATO itself, through its own strategic communications, has frequently portrayed as 'historic' events and developments that are fundamentally logical and routine military enhancement activities.

NATO’s habit of publicly presenting routine military developments in sensational terms creates a misleading impression — that the alliance is deliberately escalating tensions or seeking conflict with Russia. In reality, these measures simply address fundamental gaps resulting from two decades of lost momentum in defense planning. After all, not every defensive plan is a war plan.

* Historical details regarding the fortification are drawn from the article "Estimation of Security Threats and Estonian Defence Planning in the 1930s," authored by Estonian historian Urmas Salo and published in Acta Historica Tallinnensia (2008, Vol. 12).