The very next day, Tito received the British. He demanded military assistance and that the British Air Force bomb German concentration centers. From May 31 until June 5, the 4th Montenegrin, 7th Krajina and 10th Herzegovinian brigades fought fierce and exhausting battles with the Germans on the rugged sides of the mountain Bioč and in the upper course of the Piva. The successes achieved were insufficient, given the reserves available to the Germans. Phase IV: Supreme Headquarters in encirclement (4 June – 9 June) As the attempt to break through the front via Foča failed, the Supreme Headquarters had to return to its initial positions, which the Germans used to make an even stronger ring. In addition to the daily fighting, the Sutjeska canyon was bombarded by planes every day, in a very low flight. On June 3, Tito crossed the Piva near Mratinje with the Supreme Headquarters. Thus, in the first days of June, the entire Supreme Headquarters found itself encircled, together with the central hospital in the Sutjeska valley. On the same day, at the session of the Supreme Staff, the position of the Partisan groups with the hospital was discussed, and it was concluded that the situation was critical. The Supreme Headquarters saw that the main operational group could only break toward the west, through the Sutjeska valley because there were weaker German forces there. However, the Germans foresaw this development, so they hurried to fortify the entire Sutjeska valley. Having established that this direction, through the source part of Sutjeska and Gatačko Polje, was densely occupied in depth, the Supreme Headquarters decided to divide Partisan forces into two parts. The first group consisted of the 1st and 2nd Divisions, which had already forced Piva, with the Supreme Headquarters, and the second of the 3rd (in a slightly changed composition) and the 7th Division, with the Central Hospital and part of the councillors of AVNOJ, located east of Piva. The second group was led by Milovan Đilas, as a delegate of the Supreme Headquarters, and Sava Kovačević, who was appointed commander of the 3rd Division. The two groups were to break through in divergent directions in order to stretch the German forces. The first group was to break through Sutjeska to the northwest, while the second was given the task of returning to the right bank of the Tara, toward Sandžak. The First Proletarian Division was sent