Complex sentence: Upon finding out about Paulus' surrender, Hitler flew into a rage, and vowed never to appoint another field marshal again, though he would in fact go on to appoint another seven field marshals during the last two years of the war.
Split into simpler sentences: Upon finding out about Paulus' surrender, Hitler flew into a rage, and vowed never to appoint another field marshal again. He would, in fact, go on to appoint another seven field marshals during the last two years of the war.