He 111. The Blenheim had only a small speed advantage to overtake a German bomber in a stern-chase. Added to the fact an interception relied on visual sighting, a kill was most unlikely even in the conditions of a moonlit sky. The Boulton Paul Defiant, despite its poor performance during daylight engagements, was a much better night fighter. It was faster, able to catch the bombers and its configuration of four machine guns in a turret could (much like German night fighters in 1943–1945 with Schräge Musik) engage the German bomber from beneath. Attacks from below offered a larger target, compared to attacking tail-on, as well as a better chance of not being seen by the crew (so less chance of evasion), as well as greater likelihood of detonating its bomb load. In subsequent months a steady number of German bombers would fall to night fighters. Improved aircraft designs were in the offing with the Bristol Beaufighter, then under development. It would prove formidable but its development was slow. The Beaufighter had a maximum speed of , an operational ceiling of , a climb rate of per minute, and its battery of four Hispano cannon and six .303 in Browning machine guns was much more lethal. On 19 November, John Cunningham of No. 604 Squadron RAF shot down a bomber flying an AI-equipped Beaufighter, the first air victory for the airborne radar. In November and December 1940, the Luftwaffe flew 9,000 sorties against British targets and RAF night fighters claimed only six shot down. In January 1941, Fighter Command flew 486 sorties against 1,965 made by the Germans. Just three and twelve were claimed by the RAF and AA defences respectively. In the bad weather of February 1941, Fighter Command flew 568 sorties to counter the Luftwaffe which flew 1,644 sorties. Night fighters could claim only four bombers for four losses. By April and May 1941, the Luftwaffe was still getting through to their targets, taking no more than one- to two-percent losses per mission. On 19/20 April 1941, in honour of Hitler's 52nd birthday, 712 bombers hit Plymouth with a record 1,000 tons () of bombs. Losses were minimal. In the following month, 22 German bombers were lost with 13 confirmed to have been shot down by night fighters. On 3/4 May, nine were shot down in one night. On 10/11 May, London suffered severe damage, but 10 German