the three coordinates (range, altitude, and azimuth) of an aircraft flying at heights between 4,000 and 7,000 meters could be determined at up to 25 km distance, but with poor accuracy. Also, with the antennas aimed at a low angle, ground clutter was a problem. However unsuitable for gun-laying applications, it did show the way for future systems. An operating feature, however, rendered Zenit unsuitable for gun laying for attacking fast-moving aircraft. A null-reading method was used for analyzing the signals; azimuth and elevation coordinates had to be acquired separately, requiring a sequence of antenna movements that took 38 seconds for the three coordinates. Work at the LEMO continued on Zenit, converting it into a single-antenna system designated Rubin. This effort, however, was disrupted by the invasion of the USSR by Germany in June 1941. In a short while, all of the critical industries and other operations in Kharkov were ordered evacuated far into the East. Wartime When the German blitzkrieg swept into the Soviet Union in June 1941, three massive, tank-led Army groups moved in on a front with Leningrad, Moscow, and the Ukraine region as objectives. There followed what became known to the Soviets as the Great Patriotic War. The Komitet Oborony (Defense Committee – the small group of leaders surrounding Stalin) gave first priority to the defense of Moscow; the laboratories and factories in Leningrad were to be evacuated to the Urals, to be followed by the Kharkov facilities. Several different radar systems were produced by the Soviet Union in the relocated facilities during the war. supplemented by some 2,600 radar sets of various types under the Lend-Lease Program. Ground-based The Sveltana Factory in Leningrad had built about 45 RUS-1 systems. These were deployed along western borders and in the Far East. Without ranging capability, however, the military found the RUS-1 to be of little value. When air attacks on Leningrad began, the RUS-2 test unit assembled at the Toksovo experimental site was pressed into tactical operation, providing early-warning of Luftwaffe (German Air Force) formations. With a range up to 100 km, this unit gave timely information to civil defence and fighter networks. This gained the attention of authorities, who previously had shown little interest in radio-location equipment. In mid-July, the radio-location activities of the LEPI and NII-9 were sent to Moscow where they were combined with existing units of the NIIIS-KA. A RUS-2 system was set