The ship served with her three sister ships for the majority of World War I. She saw extensive service in the North Sea, where she took part in several fleet sorties. These culminated in the Battle of Jutland on 31 May – 1 June 1916, where "Posen" was heavily engaged in night-fighting against British light forces. In the confusion, the ship accidentally rammed the light cruiser SMS "Elbing", which suffered serious damage and was scuttled later in the night.