Complex sentence: Each of the Territorial Force battalions volunteered for service overseas and raised a second battalion, the six battalions being numbered 1/4th, 2/4th, 1/5th, 2/5th, 1/6th, and 2/6th.
Split into simpler sentences: Each of the Territorial Force battalions volunteered for service overseas and raised a second battalion. The six territorial battalions were numbered 1/4th, 2/4th, 1/5th, 2/5th, 1/6th, and 2/6th.