Complex sentence: Heavy casualties since the start of Overlord had resulted in a critical shortage of infantry replacements, and even before the crisis situation created by the Ardennes Offensive, steps were taken to divert men from Communications Zone units.
Split into simpler sentences: Heavy casualties since the start of Overlord resulted in a critical shortage of infantry replacements, and even before the crisis situation created by the Ardennes Offensive. Steps were taken to divert men from Communications Zone units.