Complex sentence: The British used the opportunity given them by the attack on Coventry to try a new tactic against Germany, which was carried out on 16 December 1940 as part of Operation Abigail Rachel against Mannheim.
Split into simpler sentences: The British used the opportunity given them by the attack on Coventry to try a new tactic against Germany. Which was carried out on 16 December 1940 as part of Operation Abigail Rachel against Mannheim.