Abstract: Japan today faces security challenges unprecedented in the post-Cold War era. As it has done when reacting to past challenges, Tokyo is responding to the contemporary security challenges primarily by investing in its military capabilities and in its alliance with the United States. It is, however, making its investments in new and unprecedented ways. This article focuses on two such unprecedented ways in which Japan is investing in the Japan–US alliance. It makes two core arguments. First, the article identifies a Japanese push for industrial and operational military integration with its US ally and argues that Japan has made substantial political, legal and institutional preparations to move the alliance beyond its traditional boundaries. Second, it argues that missile defence and counter-A2/AD (anti-access/area denial) capabilities are two prospective expressions of the new frontiers of the Japan–US alliance.