After escaping a Haganah abduction attempt, he returned to Tel Aviv, where he served in command positions. In July 1945, Dresner took part in an Irgun operation to blow up the Yibne railway bridge, and in November 1945, he participated in the Night of the Trains, a joint operation between the Irgun, Lehi, and Palmach (the elite strike force of the Haganah, which had since switched sides). Dresner was part of an Irgun unit that attacked the Lydda railway station, during which several locomotives and a number of buildings were blown up, and in which an Irgun fighter, two British security personnel, and four Arabs were killed. Dresner went on to serve as a senior Irgun commander in Ramat Gan and Petah Tikva. He personally participated in a February 1946 raid against the RAF airbase at Lydda in which several British military aircraft were destroyed, and an April 1946 arms raid against a Ramat Gan police station which saw a large amount of arms and munitions seized. During that raid, an Arab constable and two Irgun fighters were killed, and one, Dov Gruner, who would later hang alongside Dresner, was wounded and captured. Dresner was also involved in railway sabotage operations, planting mines on railway tracks to derail trains. On December 29, 1946, Dresner participated in the Night of the Beatings, an Irgun operation in which British soldiers were abducted and whipped in retaliation of the whipping of an imprisoned Irgun member. The car he and his teammates were traveling in ran into a British roadblock. In the ensuing exchange of fire, one Irgun man, Avraham Mizrahi, was killed and the remaining four taken prisoner. Following their captivity, Dresner and his surviving teammates were initially imprisoned together in a paratrooper's camp, where, according to a report Dresner later smuggled out of prison through scraps of paper to Irgun commander Menachem Begin, they were repeatedly subjected to severe beatings and humiliations by their captors. After five days, they were transferred to the Jerusalem Central Prison, where they joined Dov Gruner, who was already under sentence of death. On February 10, 1947, they were tried before a British military court, and convicted. During the trial, they refused to participate in the proceedings and denied the authority of the court to try them. Dresner, Mordechai Alkahi, and Eliezer Kashani were sentenced to death, while Haim Golevsky, who was 17 and thus too young to be hanged under the law, was sentenced to life imprisonment.