Mieczysław Dziemieszkiewicz, alias Rój, was born to a patriotic family in Zagroby on 25 January 1925. He was the son of Adam and Stefania, née Świerczewska. In 1939, he finished the primary school in Różan. During the German occupation, young as he was, he engaged in the underground activity undertaken by the National Armed Forces. In the spring of 1945, he was drafted into the Polish People’s Army, but he deserted on hearing that his brother died – Lt. Roman Dziemieszkiewicz, alias Pogoda, was murdered by Soviet soldiers in November 1945.
Mieczysław Dziemieszkiewicz enlisted as a soldier with the 16th District of the National Military Union (Northern Mazovia), adopting the pseudonym “Rój”. From 1946, at the time of mass arrests made by the secret police, he was in command of a detachment of the Special Action Unit of the National Military Union in the administrative district of Ciechanów. Soon, he was awarded the Cross of Valour for his bravery.
In 1948, he was promoted to the rank of Senior Sergeant. He performed dozens of actions against the officials of the Communist Party, the officers of the terror apparatus, and secret police confidants. He was also involved in raiding the communist secret service prison in Pułtusk (25/26 November 1946) and releasing his sixty five colleagues detained there. On 6 November 1949, in the town of Gołotczyzna near Ciechanów, he stopped a passenger train – his soldiers handed out anticommunist leaflets, and the commander himself delivered an anti-Soviet speech. Educating the society conquered by the Soviet occupant was one of Mieczysław Dziemieszkiewicz’s ways of combat.