The Japanese began to embark more nighttime bombing raids against Chongqing in summer of 1939 in effort to reduce confrontation and casualties from defending Chinese Air Force fighters, however the Chinese pilots began operating nighttime interceptions over Chonqing with some success in shooting-down the nighttime bombers using "lone wolf" fighter tactics previously deployed during the Battle of Nanking two years earlier (and similar to the "Wilde Sau" tactics the Luftwaffe would deploy a few years later), and involves the coordination with a series of manually-operated ground based searchlights illuminating and tracking incoming bombers which can then be seen and targeted by the solitary fighter pilot; fighter ace shot down a bomber in the night of 3 August, 1939 over Chonqing flying "lone wolf" in an I-15bis during such a nighttime intercept mission, among several kills he participated in claiming while battling in defense of Chongqing. In the following night, Capt. Cen Zeliu would also claim a nighttime-kill of a bomber while at the controls of an I-15bis.