Complex sentence: Approximately 1,000 of the 1,900 men on board were killed or injured and one No.9 Squadron RAF Lancaster was severely damaged by flak; it landed safely in neutral Sweden with its crew unhurt.
Split into simpler sentences: Approximately 1,000 of the 1,900 men on board were killed or injured. One No.9 Squadron RAF Lancaster was severely damaged by flak; it landed safely in neutral Sweden with its crew unhurt.