The last major attack on London was on 10/11 May 1941, on which the Luftwaffe flew 571 sorties and dropped 800 tonnes of bombs. This caused more than 2,000 fires. 1,436 people were killed and 1,792 seriously injured, which affected morale badly. Another raid was carried out on 11/12 May 1941. Westminster Abbey and the Law Courts were damaged, while the Chamber of the House of Commons was destroyed. One-third of London's streets were impassable. All but one railway station line was blocked for several weeks. This raid was significant, as 63 German fighters were sent with the bombers, indicating the growing effectiveness of RAF night fighter defences.