bed), each covering an area some 45 km wide and 30 km deep, and containing a radar, several searchlights, and a primary and backup night-fighter aircraft. This was relatively effective except when the sky was overcast. A new gun-directing radar was needed to cover this deficiency and the Luftwaffe then contracted with Telefunken for such a system. Under the leadership of Wilhelm Runge, the new radar was built by Telefunken around a new triode capable of delivering 10-kW pulse power at 60 cm (500 MHz). Code-named Würzburg (the leading engineer Runge prefers code-names of German cities like Würzburg), this had a 3-m (10-ft) parabolic reflector supplied by the Zeppelin Company and was effective at a range of about 40 km for aircraft. Two of these radars were normally added to each Himmelbett, one to pick up the target from a Freya and a second to track the fighter aircraft. Requiring only one operator, the Würzburg came to be the primary mobile, gun-laying system used by the Luftwaffe and Heer during the war. About 4,000 of the various versions of the basic system were eventually produced. The Air Defense System was continually upgraded. To improve the range and accuracy, Telefunken developed the Würzburg-Riese and GEMA enlarged the Freya dipoles to make the Mammut and the Wassermann. The Würzburg-Riese (Giant Würzburg) had a 7.5-m (25-foot) dish (another product from Zeppelin) that was mounted on a railway carriage. The system also had an increased transmitter power; combined with the enlarged reflector, this resulted in a range of up to 70 km, as well as greatly increased accuracy. About 1,500 of this radar system were built. The Mammut (mammoth) used 16 Freyas linked into a giant 30- by 10-meter (100- by 33-foot) antenna with phased array beam-directing, a technique that would eventually become standard in radars. It had a range up to 300 km and covered some 100 degrees in width with an accuracy of near 0.5 degree. About 30 sets were built, some with back-to-back faces for bi-directional coverage. The Wassermann (waterman), had eight Freyas also with phased-array antennas, stacked on a steerable, 56-meter (190-foot) tower and giving a range up to 240 km. A variant, Wassermann-S, had the radars mounted on a tall cylinder. About 150 of all types were built starting in 1942. A system with great range was needed to track the British and American bomber formations as they crossed