Complex sentence: Many sections of the S-Bahn were closed during the war, both through enemy action and flooding of the Nord-Süd-Bahn tunnel on 2 May 1945 during the final Battle of Berlin.
Split into simpler sentences: Many sections of the S-Bahn were closed during the war owing to enemy action. The Nord-Süd-Bahn tunnel was flooded on 2 May 1945 during the final Battle of Berlin.