Construction of the fortifications began in June, 1939 around the village of Wizna in northeast Poland. With war clouds gathering just beyond its border with Germany, the government worked its laborers hard to complete the nine kilometers long defensive positions overlooking the swampy Narew River valley. This area was considered vital, as it defended the Narew and Biebrza river crossings as well as twin roads which led to the rear of a force assigned to the region.
Known as “Independent Operational Group Narew,” it consisted of a corps-sized unit tasked with holding the frontier near the Lithuanian border. One of its subordinate units, the 71st Infantry Regiment, lent a battalion supplemented by an MG company from the ‘Osowiec Fortress’ unit to staff the growing concrete bunkers, pillboxes, and trenches stretching out on the hills behind Wizna throughout the summer months of that fateful year.
The types of structures that went up around them appeared quite formidable, ranging from heavy concrete bunkers with steel cupolas housing anti-tank and machine guns, to smaller concrete MG pillboxes, to positions protected by nothing more than earthworks and sandbags. Added to this were minefield, anti-tank and anti-personnel obstacles and rows of concertina wire that coursed around the different sites. On paper, the original plan called for sixty of these various emplacements to be positioned over a 9 kilometer breadth, but as time wound down to September 1st, only sixteen of the strongpoints had been completed. Moreover, they contained a flaw that, despite the heroism destined for display in and around them in the coming days, ultimately would prove their undoing.
This flaw was simple, and shall be described further into the story.