The army commander, General Ernest de Cissey, began a systematic siege and a heavy bombardment of the fort that lasted three days and three nights. At the same time Cissey sent a message to Colonel Megy, with the permission of Marshal MacMahon, offering to spare the lives of the fort's defenders, and let them return to Paris with their belongings and weapons, if they surrendered the fort. Colonel Megy gave the order, and during the night of 29–30 April, most of the soldiers evacuated the fort and returned to Paris. But news of the evacuation reached the Central Committee of the National Guard and the Commune. Before General Cissey and the Versailles army could occupy the fort, the National Guard rushed reinforcements there and re-occupied all the positions. General Cluseret, commander of the National Guard, was dismissed and put in prison. General Cissey resumed the intense bombardment of the fort. The defenders resisted until the night of 7–8 May, when the remaining national guardsmen in the fort, unable to withstand further attacks, decided to withdraw. The new commander of the National Guard, Louis Rossel, issued a terse bulletin: "The tricolor flag flies over the fort of Issy, abandoned yesterday by the garrison." The abandonment of the fort led the Commune to dismiss Rossel, and replace him with Delescluze, a fervent Communard but a journalist with no military experience.