Complex sentence: During the same time the firepower of a brigade was increased by the assignment of more machine guns, eventually as the war progressed, a brigade had their own machine gun company and a trench mortar battery assigned.
Split into simpler sentences: During the same time, the firepower of a brigade was increased by the assignment of more machine guns. Eventually, as the war progressed, a brigade had its own machine gun company and a trench mortar battery assigned.