of coal to the Greater London regions and urgent repairs were required. Attacks against East End docks were effective and many Thames barges were destroyed. The London Underground rail system was also affected; high explosive bombs damaged the tunnels rendering some unsafe. The London Docklands, in particular, the Royal Victoria Dock, received many hits and Port of London trade was disrupted. In some cases, the concentration of the bombing and resulting conflagration created firestorms of 1,000 °C. The Ministry of Home Security reported that although the damage caused was "serious" it was not "crippling" and the quays, basins, railways and equipment remained operational. Improvements in British defences British night air defences were in a poor state. Few anti-aircraft guns had fire-control systems, and the underpowered searchlights were usually ineffective against aircraft at altitudes above . In July 1940, only 1,200 heavy and 549 light guns were deployed in the whole of Britain. Of the "heavies", some 200 were of the obsolescent type; the remainder were the effective and guns, with a theoretical "ceiling"' of over but a practical limit of because the predictor in use could not accept greater heights. The light guns, about half of which were of the excellent Bofors 40 mm, dealt with aircraft only up to . Although the use of the guns improved civilian morale, with the knowledge the German bomber crews were facing the barrage, it is now believed that the anti-aircraft guns achieved little and in fact the falling shell fragments caused more British casualties on the ground. Few fighter aircraft were able to operate at night. Ground-based radar was limited, and airborne radar and RAF night fighters were generally ineffective. RAF day fighters were converting to night operations and the interim Bristol Blenheim night fighter conversion of the light bomber was being replaced by the powerful Beaufighter, but this was only available in very small numbers. By the second month of the Blitz the defences were not performing well. London's defences were rapidly reorganised by General Pile, the Commander-in-Chief of Anti-Aircraft Command. The difference this made to the effectiveness of air defences is questionable. The British were still one-third below the establishment of heavy anti-aircraft artillery AAA (or ack-ack) in May 1941, with only 2,631 weapons available. Dowding had to rely on night fighters. From 1940 to 1941, the most successful night-fighter was the Boulton Paul Defiant; its four squadrons shot down