Complex sentence: By 14:00 the 4th Parachute Brigade was no further forward and with casualties mounting Brigadier Hackett, asked General Urquhart's permission to withdraw south of the railway line.
Split into simpler sentences: By 14:00 the 4th Parachute Brigade was no further forward. With casualties mounting, Brigadier Hackett asked General Urquhart's permission to withdraw south of the railway line.