Complex sentence: He was detailed to take a patrol over the lines at 06:00 but at 05:00, during the mission briefing, around 100 German bombers with fighter escort attacked the capital, seeking to attack Allied shipping in the harbour.
Split into simpler sentences: He was detailed to take a patrol over the lines at 06:00. However, at 05:00, during the mission briefing, around 100 German bombers with fighter escort attacked the capital, seeking to attack Allied shipping in the harbour.