It was a war of attrition for the Chinese pilots, as many of their most experienced ace fighter pilots, such as Lieutenant , Colonel Kao Chih-hang, Yue Yiqin, among others, were lost; six months into the war, the Chinese Air Force inventory of frontline American Hawk IIs and IIIs and P-26Cs, and various others, were mostly superseded by faster and better armed Polikarpov I-15s and I-16s provided under the Sino-Soviet Treaty of 1937, including Soviet volunteer combat aviators. However, with the Fall of Nanking, the Fall of Wuhan, and the losses at the Battle of South Guangxi, the primary supply-line of China's "war of resistance" against the Imperial Japanese aggressions was dealt a further blow, not least of which the high-octane aviation fuel that was blocked-off from Chinese access, but still accessible to Imperial Japan.