Complex sentence: The position had two trenches about apart, with sentry garrisons to occupy the front trench, with the main line of defence in the second line, which was equipped with dug-outs for most of the front garrison.
Split into simpler sentences: The position had two trenches about apart, with sentry garrisons to occupy the front trench. The main line of defence was the second line, which was equipped with dug-outs for most of the front garrison.