Poland's military and political ties with France did not always translate to Polish adoption of French practices; many Polish generals resented French claims that the French observers took a direct hand and “won” the climactic Battle of Warsaw in 1920. Polish doctrine drew on many sources, chiefly their own experiences of the war with the Soviets and in the German, Austrian and Russian armies during World War One. As a result, the Poles did not place the same faith in fixed fortifications as did the French, only beginning widespread construction in the spring of 1939. One of the new fortified zones was along the southern border, made vulnerable by the German takeover of Czechoslovakia.

Fighting raged around the bunker positions for 24 hours, until the Germans had stormed them all and killed or driven off the defenders. Ordered to abandon the line and withdraw, the Poles instead stood their ground and fought with a berserk fury; most died at their posts. Parts of a National Guard battalion helped screen the retreat of the survivors.