He took part in the Invasion of Poland in 1939, fighting against Nazi Germany. He was captured and sent to a POW camp from which he escaped, most likely in November 1940. After coming back to his home region he joined a small resistance group Polska Organizacja Zbrojna which later became part of the Polish Home Army. He was made the commander of a 35 men platoon in the sub-region of Stary Radzic, AK Region "Lubartów", in the Inspectorate of Lublin.
At the end of 1943, after a series of arrests of local underground anti-Nazi activists, and threatened with arrest himself, Broński organized a partisan group and "went to the forest". In May 1944 it was formally made into a flying column of the 8th Regiment of Infantry of AK Legions. Originally the column numbered 40 partisans but in the next few months it grew in numbers. During this time, the regiment was stationed in the forests around Zawieprzyce, Kozłowiec and Parczew. Also in May he was promoted to lieutenant. In June his unit was made part of the 27 Volhynian Infantry Division. On the 16th of July, the division, for which Broński's unit served in the role of scouts, found themselves surrounded by German forces, in a large scale anti-partisan action. As a result, the partisans had to quickly move to the region of Czemierniki forests. During Operation Tempest, the Broński unit took part in the fighting as the 3rd Company of the IV Battalion of the 8th Regiment "Lublin".
Back in the underground
After the Red Army entered Poland, Zdzisław managed to evade arrest. He disbanded his unit and initially declared his willingness to join the Soviet controlled People's Army of Poland. However, when he learned that he was sought after by communist authorities he went back underground. From August 1944 he served as first second in command, and then the commander of the I AK Region "Lubartów". In Winter of 1945, based on the unit that he had under German occupation, he recreated his flying column of several dozen men, which became part of the "Freedom and Independence" organization. On June 1, 1945 he was promoted to the rank of lieutenant. On May 25, 1946, the new inspector of the Win Inspectorate "Lublin" Franciszek Abraszewski made Broński the commander of the Operational Region Lubartów. As a result, all the partisan groups and squads operating in the region now came under Broński's command, and he himself came under the direct command of Major Hieronim Dekutowski. In October 1946, Uskok's group took control of Łęczna, capturing the local headquarters of the milicja, and in December, together with the unit of Leon Taraszkiewicz, in a reprisal action, his unit took part in pacification of the village of Rozkopaczew where several buildings were burned. After the new Polish authorities declared an amnesty, under the February 22, 1947 statute of amnesty, for all military groups that were still refusing to acknowledge their power, Broński seriously considered leaving the underground. In his group he left the individual decisions to his subordinates. Successive commanders of the Lublin District of WiN -col. Wilhelm Szczepankiewicz ps. "Drugak" and Franciszek Żak ps. "Wir" - had also encouraged him to come out of hiding. However eventually he decided to remain in conspiracy and still carry out military actions against the new authorities. Unfortunately his operations were aimed not only against the state officials, but also against civilians. Often his group attacked and killed those civilians who supported the new authorities or even sympatised with their actions. For example, on May 1, 1947 "Uskok's" group shoot seven members of the ZWM youth organization, who were returning from the May Day parade. Among the victims were: Paweł Budka, Zdzisław Czubacki, Zygmunt Duda, Mieczysław Jesionek, Bolesław Lipta, Bolesława Skrzypaczka and Zygmunt Żembski. However the most infamous action of his troops was the slaughter of the inhabitants of the village Puchaczów. This action was conducted by squads that were under the command of "Uskok", led by: "Wiktor", "Żelazny" and Józef Strug ps. "Ordon". In their opinion, the sufficient justification for this action was the fact that three identified inhabitants of the village gave away the location of hiding of three "Uskok's" partisans to the new authorities. Despite the fact that it was known who reported the partisans, the whole village was pacified and 21 of its inhabitants were shot. A complete list ofthe future victims was prepared beforehand. Broński himself considered the slaughter as bloody but necessary. At one point one of the sub-commanders in Broński's group was Józef Franczak who later would become the last of the "Cursed soldiers" to remain in the underground, fighting communist authorities until 1963.
