Complex sentence: He called Field Marshal Wilhelm Keitel Chief of German Armed Forces High Command (OKW) in Fürstenberg and told him that if relief did not arrive within 48 hours, all would be lost.
Split into simpler sentences: He called Field Marshal Wilhelm Keitel Chief of German Armed Forces High Command (OKW) in Fürstenberg. Krebs told Keitel that if relief did not arrive within 48 hours, all would be lost.