On the morning of 11 April, the SS commander of the Buchenwald concentration camp summoned the camp senior. The SS would withdraw at noon, he informed him, and the senior was to turn the camp and its remaining 21,000 inmates over to the U.S. Army. The inmates’ underground organization was on high alert – elsewhere, bloody massacres had not infrequently followed on the heels of such announcements. It mobilized its resistance groups, who had been preparing for months to defend themselves when this moment arose.
The first American tanks arrived around one o’clock p.m. Within 90 minutes, the 37th Tank Battalion of the 4th U.S. Armored Division had militarily defeated the SS, overrun their garrison and continued eastward. Over the next hour, the resistance groups took control of the camp, hoisted a white flag at the entry gate and, by evening, captured 76 SS men. By the time the 4th and 6th U.S. Armored Division scouts entered the camp in the late afternoon, Buchenwald was irrevocably free.
Reference: Volkhard Knigge et al. (eds.), Buchenwald: Ostracism and Violence, 1937–1945, Göttingen 2017.