the ground, barely able to mutter a sound to identify himself, and rescued four hours later, succumbing to his battle wounds the following day in a hospital. The pre-dawn attack on 4 May resulted in far more casualties, with over three thousand deaths, injuring almost 2,000 more, and leaving about 200,000 homeless. Although the attacking force was smaller and dropped fewer bombs, there was no interception of the bombers by the Chinese Air Force whose airbases in the Chongqing region were not yet set up for nighttime operations. Two months later, after tens of thousands of deaths, in retaliation for firebombing, the United States embargoed the export of airplane parts to Japan, thus imposing its first economic sanction against that nation. The Japanese began to embark more nighttime bombing raids against Chongqing in summer of 1939 in an 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). The interceptions involved 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 Liu Zhesheng shot down a bomber on the night of 3 August 1939 flying "lone wolf" in an I-15bis during such a nighttime interception mission over Chongqing, among several other kills he claimed while battling for the 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. Monks of the Ciyun Temple contributed greatly to rescuing and saving lives of residents over the course of the half-decade long bombing campaigns over Chongqing. By mid-1940, the IJNAF G3M Model 21 bombers that formed the primary aircraft of the carpet-bombing campaign against Chongqing and Chengdu had become largely relegated to nighttime bombing attacks, while daylight raids were being replaced with the new and improved Model 22/23 G3Ms equipped with the higher-octane rated and supercharged Kinsei 51 engines, boosting the power of each of the twin-engined bombers by 500 horsepower and greatly enabling the schnellbomber strategy further above the general obsolescence of the defending Chinese fighter