William Band was a British theoretical physicist, who received his M.Sc. at the University of Liverpool in 1927. In 1929, he gave up a chance to study for his Ph.D. in the Cavendish Laboratory at Cambridge University as well as a lucrative job offer from the Imperial Chemical Industries; instead, he chose to accept the call from the physics department at Christian Yenching University in Peking. Three years later, Band became the head of the department which he led for the next decade until the Japanese army shut down the university in December 1941. At Yenching University, Band not only established his career as a theoretical physicist but also made significant contributions to Chinese development in modern physics education and research, cultivating many distinguished Chinese physicists in the 20th century. After Pearl Harbor, Band narrowly escaped from Japanese-occupied Peking and sought refuge in Communist guerrilla bases, where he helped train many Chinese radio technicians. Having completed his legendary 1,000-mile trek, he arrived in Chongqing in early 1944, where he worked with Joseph Needham to aid Chinese scientists and their studies in the war. Based on archival resources in both English and Chinese, I will explore in this paper Band’s motives to relocate in Peking and discuss his transnational scientific contributions which have so far been largely overlooked.