Military exercises, as tools of foreign policy, are often overlooked in defence debates. The US–Japan amphibious military exercises that took place in January and February 2014, however, provide strong evidence that exercises can act as a significant deterrent. In this year’s iteration of the annual ‘Iron Fist’ exercise series, which began in 2006, a full company-sized contingent of approximately 250 Japanese troops from the Ground Self-Defence Force trained with the United States Marine Corps in California’s Camp Pendleton. It was the largest and most integrated US–Japan amphibious military exercise to date, and simulated the retaking of islands.

The ‘Iron Fist’ exercises are more than a confidence-building measure or an opportunity to increase interoperability: they are the testing ground for the development of Japan’s first truly amphibious force. Modelled on the US Marine Corps, this 3000-strong unit is earmarked for deployment to Sasebo in Kyushu, and constitutes an important part of Japan’s military modernisation program in the wake of growing threats to its Nansei island chain including the Senkaku/Diaoyu Islands.

Despite statements that these exercises are not aimed at any one country, China looms large on the horizon. The fear in Tokyo and Washington is that Beijing may, overtly or covertly, deploy troops and seize the Senkaku/Diaoyu Islands in a short, sharp war, presenting Japan with a fait accompli. After Japan nationalised three of the five main islands which comprise the Senkakus in September 2012, China increased its maritime presence in the East China Sea. China is also perceived as being increasingly assertive in its other territorial and maritime disputes in the South China Sea. This has prompted a new sense of purpose in Japan’s security community as evident in Prime Minister Shinzo Abe’s drive to lift Japan’s ban on collective self-defence, as well as his successful push to increase defence spending and establish the National Security Council.

By expanding the ‘Iron Fist’ exercises, both Japan and the US are signalling not only the political will to act in concert to prevent a Chinese attack, but also the demonstration of the military means to back the threat of retaliation. The exercises thus have a direct bearing on both Japanese and American deterrence capabilities. Consequently, these exercises will become an increasingly central feature of US–Japan military cooperation.

More than thirty years have passed since the first US–Japan military exercises and their number and scope have expanded considerably since then. The ‘Iron Fist’ series of combined amphibious military exercises, and particularly its latest iteration, have three features that set them apart from other exercises.

First, they provide a vital opportunity for Japan to develop a capability that it long lacked, and one that constituted one of its greatest vulnerabilities to territorial defence, alongside missile defence. In effect, the approval of the ‘dynamic defence force’ concept in the 2010 Defence White Paper was a significant step for Japan away from its Cold War military posture. The dynamic defence force idea emphasises small, high-tech, high-mobility military forces capable of responding to low intensity conflicts away from the main islands of Japan.

Second, these exercises allow the US to effectively address a major vulnerability in Japan’s military strategy within a defensive context. As such, the US can transfer relevant military capabilities and further alliance goals without unduly provoking China. The contribution of US Marines to humanitarian assistance and disaster relief operations also lessens the potential for a negative reaction by mitigating political suspicions of a military build-up directed against China.

Third, combined military exercises benefit Japanese and American deterrence without requiring significant changes in the current alliance framework. This avoids the political and bureaucratic pitfalls usually attached to alliance reform, as the difficulties surrounding the relocation of the air base in Futenma demonstrated.

Military exercises provide a platform for functional military cooperation in a way that highly politicised initiatives — such as Japan’s right to collective self-defence — simply cannot. Amphibious military exercises will become increasingly important to the US–Japan alliance and to regional security policies.

Tiago Mauricio is a WSD-Handa non-resident fellow at Pacific Forum, CSIS. He is also a graduate student at Waseda University where he is conducting research on military exercises and their strategic implications in East Asia.