Sarny Fortified Area Sarny Fortified Area ( known in Polish in several names : " Sarneński Rejon Umocniony " , " Sarneński Odcinek Umocniony " , " Bastion Polesie " ) was a line of bunkers and trenches along both sides of the Sluch river , in the area of the town of Sarny , northern Volhynia in Ukraine . In the interbellum period Sarny belonged to the Second Polish Republic , it was located close to the border with the Soviet Union . As Polish military authorities regarded the Soviets as the main threat ( see : Plan Wschod ) , in 1936 construction of fortifications began . It was planned to be fully operational in the spring of 1940 . Total length of the defence works was some 170 kilometers , number of objects - 358 . Structure . Depth of defence works was up to 5 kilometers ; they were connected by the radio , but walls of some bunkers were so thick that operators had to go outside . In every bunker there were up to 30 soldiers of the Border Defence Corps ( KOP ) ; they were equipped with 75 mm cannons and machine guns . The Border Defence Corps Regiment " Sarny " , which operated the Area , was very well trained , and its soldiers , including Władysław Raginis , distinguished themselves during the Battle of Wizna ( see Polish September Campaign ) , and in other battlefields in the area of Osowiec and Upper Silesia , where up to 80 % of KOP died or were wounded . Polish September Campaign . Those soldiers who remained in the Sarny Fortified Area were ordered in mid - September 1939 to abandon the bunkers and move with their equipment towards the Romanian Bridgehead . On September 16 , 1939 , the eve of , there were smaller units , defending the Area - two fortress battalions ( " Sarny " ) and ( " Malynsk " ) , two border battalions ( " Rokitno " ) and ( " Berezne " ) as well as a cavalry squadron " Bystrzyce " , altogether some 4000 soldiers , but lacking heavy equipment , as it had been sent towards the German border in the summer of 1939 . Defence . In the morning of September 17 , 1939 , Soviet aircraft bombed the trucks , which were getting ready to move south . Also , the railway junction in Sarny was bombed , but the Armored Train " Marszalek " repelled the enemy . Despite this , Colonel Nikodem Sulik and General Wilhelm Orlik - Rueckemann decided to unload the stuff and take up defence positions . The Sarny Fortified Area was attacked by the Soviet 60th Rifle Division , whose advantage was crushing . The Poles defended the fortifications for three days , on September 20 , facing encirclement , they had to withdraw . However , soldiers in some bunkers did not get the order to withdraw , and in some places the Poles resisted until September 25 . Several bunkers were blown up by the Red Army engineers with their crews , unknown number of soldiers were murdered , including seven officers , who were shot near the Orthodox church in the village of Tynne . Among those killed was Lt . Jan Bolbot , who was in 1989 posthumously awarded the Virtuti Militari , Poland ’ s highest military decoration . He commanded a platoon of 50 men , who holed up in their bunker and refused to surrender despite hopeless odds . Bolbot ' s men stopped Soviet attacks with heavy losses . Unable to beat the Poles , the Soviets set the bunker on fire . Bolbot and his entire command died in the flames . In late September , the defenders of Sarny , as part of Independent Operational Group Polesie , took part in two major battles against the Red Army - Battle of Szack and Battle of Wytyczno . Aftermath . In late 1939 and early 1940 the Soviets carried out detailed investigations of the defence works . In mid - 1940s , the bunkers served as a hideout for Ukrainian nationalist partisans of the Ukrainian Insurgent Army . Today , the bunkers are in ruin .