Complex sentence: As a result, the 146th Infantry Brigade formed a duplicate unit, to be known as the 138th Infantry Brigade and was assigned to the 46th Infantry Division, itself formed as a duplicate of 49th (West Riding) Infantry Division.
Split into simpler sentences: As a result, the brigade number was activated again when the 146th Infantry Brigade formed a duplicate unit, to be known as the 138th Infantry Brigade. The new brigade was assigned to the 46th Infantry Division, itself formed as a duplicate of 49th (West Riding) Infantry Division.