Complex sentence: Groups of soldiers, known in the British army as wiring parties went out at night into no man's land to position these supports and then to string the barbed wire through the loops to form a defensive wire obstacle as a protection for their trench line.
Split into simpler sentences: Groups of soldiers, known in the British army as wiring parties went out at night into no man's land to position these supports. They later strung the barbed wire through the loops to form a defensive wire obstacle as a protection for their trench line.