Complex sentence: The squadron attempted to improve their defences, but thirty minutes later around 1,000 Turks had surrounded, and attacked, the post and by 23:30 had cut the telephone wires to the rest of the brigade.
Split into simpler sentences: The squadron attempted to improve their defences, but thirty minutes later a force of around 1,000 Turks had surrounded, and attacked, the post. Then by 23:30 had cut the telephone wires to the rest of the brigade.