Complex sentence: The next day they moved to the left flank in the north to relieve the Royal Naval Brigade, in their trenches that stretched from the sea to Walkers Ridge and two outposts No.1 Post and No.2 Post.
Split into simpler sentences: The next day they moved to the left flank in the north to relieve the Royal Naval Brigade. Their trenches stretched from the sea to Walkers Ridge and included two outposts No.1 Post and No.2 Post.