Before all the prisoners could be evacuated what happens? (Chapter 9)

On April 10, the remaining 20,000 prisoners are to be evacuated and the camp blown up. A siren alert occurs, however, and the evacuation is postponed to the next day. Nobody had eaten anything for six days. The next morning the resistance movement suddenly battles the SS in the assembly place. The SS flees, and resistance takes charge of the camp. At six in the evening, the first American tank arrives at Buchenwald.