Since 2007, Australia and Japan have steadily broadened and deepened their security relationship. When considering the drivers behind this development, analysts have argued that it is the presence of the US that makes the bilateral security relationship between Australia and Japan matter. In 2014–16, assumptions underpinning this security relationship in Australia and Japan were exposed when Japan bid unsuccessfully for Australia’s Future Submarine contract. As the competitive process unfolded, it became clear that Australia and Japan held dissonant views about each other’s worth and motivations. In particular, policy makers and commentators in each country disagreed about the desirability and rationale for upgrading their security relationship to an alliance. This chapter assesses the implications of these different perspectives and what they tell us about the actual foundations and prospects for bilateral security policy ambitions in the Asia Pacific and beyond.