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.