In this chapter, I discuss the activities of South Korean military band musicians as one of the groups who played a key role in these musical developments that transcended the military context and wartime. In particular, I examine the military band musicians’ creation and performance of Korean military marches, exploring their implications for musical nationalism in South Korea, and their performance of popular music with its contributions to the emergence of new popular music practices in South Korea within the transnational Cold War context. Ultimately, I argue that it was the versatility of South Korean military band musicians in fulfilling the functions of military music, as well as their positions in both the field of music and the social field of the Korean War, that made it possible for them to be significant agents of musical formations in South Korea during and after the war, spreading their influence beyond the boundaries of the military sector.