Complex sentence: When he learned that the Americans had stopped to regroup, rest and wouldn't take the city until later, Schwerin tried to retrieve the message but the message had been forwarded to Field Martial Walter Model, Schwerin's commander.
Split into simpler sentences: When he learned that the Americans had stoped to regroup, rest and wouldn't attack the city untill later, Schwerin tried to retrieve the message but was too late. The message had been forwarded to Field Martial Walter Model, Schwerin's commander.