Complex sentence: The 6th Airlanding Brigade advance started along two axes, with the 12th Devons on the left, the 2nd OBLI on the right, and the 1st RUR in reserve.
Split into simpler sentences: The 6th Airlanding Brigade advance started along two axis. The 12th Devons was on the left and the 2nd OBLI on the right, with the 1st RUR in reserve.