During the Imjin War (1592–1598), a new type of warfare centered on the harquebus was introduced into Korea. This led to the formation of a new infantry-based military composed largely of harquebusiers. Existing scholarship on the military change of Korea in this period has primarily focused on the emergence of the standing army. However, most of the troops were militiamen, similar to those of the prewar military. This article examines the broader contours of Korea’s military organization during this transformative period, with particular attention to the composition and roles of the forces. To be sure, a new standing army unit was organized, but its proportion was small both in absolute numbers and in participation in actual warfare. Instead, the militia continued to constitute the core of the Korean military and carried out the majority of wartime operations. The Korean court did not intend to raise a standing army as the new center of military power. This was due to its strong ideological commitment to the militia system and the actual military environment that Korea was facing. The Korean case presents a distinctive example of how the introduction of harquebus could coexist with the persistence of militia-based military structures.