On May 11, 1944, forty thousand troops from the Chinese Expeditionary Force (CEF), or Y Force, as the Americans called it, crossed the Salween River to retake southwest China from the Japanese. The Salween was rapid and unnavigable, a turbulent river between two colossal mountain ranges. The Chinese called it Nujiang (怒江), or “Angry River.” General Xiao Yisu, the CEF’s chief of staff, worried that his troops would be unable to cross it. He brought his worries to Colonel Frank Dorn, head of the Y Force Operations Staff (YFOS), an American advisory mission which assisted the CEF throughout the campaign. Dorn assured him it was possible and his staff trained Chinese troops on the nearby Mekong River. At midnight on the early morning of May 11, the first wave of soldiers pushed out into the Salween. It was a tense moment – their equivalent to the Normandy landings. But far from the disaster General Xiao feared, only one man was lost in the crossing and the landings on the west bank went largely uncontested; the Japanese did not believe they could push over the twelve-thousand-foot-tall Gaoligong Mountains and so left the river undefended. With firm bridgeheads thus established, the CEF moved reinforcements across and began the tortuous trek into the mountains. It was the beginning of one of the most arduous campaigns of World War II – one which saw Chinese and Americans working together on the highest battlegrounds of the war.