While the bulk of the U.S. forces advanced east towards the Elbe river, some 18 U.S. divisions remained behind to destroy the isolated forces of Army Group B. The reduction of the German pocket was begun on 1 April by the U.S. Ninth Army, with the forces of the U.S. First Army joining on 4 April. For 13 days the Germans delayed or resisted the U.S. advance. On 14 April, the First and Ninth Armies met, splitting the German pocket in half and German resistance began to crumble.