The receiver of the initial Zenit system was not sufficiently sensitive, and was redesigned by Truten using a 955 acorn triode from RCA. In September 1940, Slutskin demonstrated the revised Zenit to the Red Army and Red Navy, detecting aircraft at ranges up to 25 km. This was the first full three-coordinate, radio-location system in the Soviet Union. However, the time required to measure the coordinates (distance, azimuth, and elevation) was too long for gun-laying in anti-aircraft batteries. Although not accepted by the military, the Zenit did show the way for further developments.