Complex sentence: On mobilization, the Bavarian Army formed twelve Brigade Replacement Battalions ("Brigade-Ersatz-Bataillone ") by grouping companies taken from the replacement, or"Ersatz", battalion of each infantry regiment.
Split into simpler sentences: On mobilization, the Brigade Replacement Battalions ("Brigade-Ersatz-Bataillone ") of the Bavarian Army were formed. A brigade replacement battalion was formed by grouping companies taken from the replacement, or"Ersatz", battalion of each infantry regiment.