20 November 2023

Evolving Japan-US command and control cooperation for forward denial

This article was commissioned as part of the Japan-Australia-United States trilateral security study project, Assessing the implementation of Abe's National Security Strategy
Japan Ground Self-Defense Force's Amphibious Rapid Deployment Brigade conducts a military drill in Gotemba at the foot of Mt. Fuji, during a joint aerial maneuver training with the US Marine Corps' 31st Marine Expeditionary Unit. 15 March 2022.Source: Getty
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Japan’s 2022 National Security Strategy, National Defense Strategy, and Defense Build-Up Plan pledged to modernise the country’s defence capabilities, mainly focusing on acquiring new hardware including long-range missiles and unmanned assets. While Japan’s allies, including the United States, have received these commitments positively with the expectation that Japan will play a critical role in a potential Taiwan contingency, it is still unclear how the Self-Defense Forces (SDF) would plan to fight with its newly acquired capabilities. Japan needs to develop the details of the ‘software’ (operational concepts and doctrines) required to operate the acquired “hardware” (weapons and equipment). One of the key components of this is the modernisation of the joint command structure of the SDF and its cooperation with its US counterpart, particularly with the assumption to deal with a potential by mainland China Taiwan contingency, given it is a possible contingency with the state both Japan and the United States perceive as “the greatest strategic challenge” or “the most comprehensive and serious challenge” to their national security.

In this commentary, I argue that SDF’s joint command structure and its command and control (C2) cooperation with the United States need to be updated to account for its planned shift in force posture and force structure. The 2022 strategic documents started to shift Japan’s defence posture from territorial defence toward, what I call, ‘forward denial’ by degrading enemy forces in the distant area from Japanese territory. This shift will blur two distinctions that have typically been clear in Japanese military thinking: the geographical distinction between the three services in the SDF, and the functional distinction between the SDF and US forces. These blurred distinctions will require stronger C2 integration both among the three SDF services and between the United States and Japan. I will also present some policy recommendations to strengthen this C2 integration.

SDF’s joint command structure and its command and control cooperation with the United States need to be updated to account for its planned shift in force posture and force structure

Integrated command and control for forward denial

Japan’s strategic documents detail how the country aims to acquire new defence capabilities, including stand-off missiles, “to disrupt and defeat invasion at earlier timing and locations further afield.” By doing so, Japan will seek to “ensure asymmetric advantage” for the SDF against adversary forces, according to its National Defense Strategy. This is a significant and substantial departure from Japan’s long-standing principle of ‘the Exclusively Defense-Oriented Policy,’ a passive territorial defence posture adopted in accordance with the spirit of the Japanese Constitution. Although the Japanese Government does not explicitly name it, we could term this new setting ’forward denial posture.’1 However, to successfully implement Japan’s tacit forward denial posture will require a higher level of integration among the three SDF component forces – the Ground-, Air- and Maritime-Self Defense Forces, respectively. As it stands, the current SDF C2 structure has not been fully optimised for this requirement.

Since its establishment in 1954, the SDF has never conducted any joint combat operations. Although the Joint Staff has supervised major service components of the SDF in a coordinated manner, its peacetime operations, such as intelligence, surveillance, and reconnaissance (ISR) operations, do not necessarily require a high level of integration between different services’ forces in the field. The field autonomy of operations is thus delegated to the commander of the component force depending on the mission; for example, the commander of the Self-Defense Fleet in the case of maritime surveillance missions, and the commander of the Air Defense Command in the case of air defence missions. In addition, during a contingency, the joint task force (JTF) commander is supposed to be temporarily assigned to the top commander of a component force deemed most suitable for individual missions by the creation of the JTF. This means that, on the one hand, there is no standing joint staff body at the force level and, on the other hand, that the actual command and control of subordinating forces is delegated to the temporary joint task force commander, since the Joint Staff cannot control everything on the field.

As newly acquired capabilities are introduced into the SDF, this dependence on the temporary JTF commander and major component commands will no longer be tenable. This is partly because the geographical distinction in operations among the three SDF services will be blurred, as all of the Ground, Maritime, and Air Self-Defense Forces will acquire stand-off missiles and unmanned assets aimed at operating in distant areas. That means every service may have the capabilities to support the others while that service may itself be supported by the others in a cross-domain setting. Consequently, autonomous operations within a single domain and the delegation of field C2 to the respective major component commanders will be more and more difficult. Complex and real-time fire coordination and avoiding fratricides among missiles, aircraft, naval vessels, and drones will also be necessary. The lack of standing staff members for the joint operational commander may create a deficiency in coordinating such highly specialised C2-related work.

In addition, although the Chief of the Joint Staff is the highest-ranking general throughout the SDF, most of the officers at the middle level of the Joint Staff, who are expected to be the core of operational planning in contingencies, are usually in junior positions vis-à-vis the staff members at the major component forces. This may make it difficult for the Joint Staff to exercise strong guidance over component forces. On the other hand, the temporarily designated JTF commander and its command staff will have difficulty in dealing with other services’ major commands because, during peacetime, there is no standing hierarchical C2 chain among them.

These are among the reasons why Japan is establishing the Permanent Joint Headquarters (PJHQ), as recommended by the 2022 strategic documents. However, while it will be established by the end of FY2024 with 240 staff personnel, the specific design of the organisation is still unclear. As such, based on the argument above, the following two factors need to be highlighted when considering the design of the PJHQ.

Firstly, middle-level standing staff members comprising subject matter experts in joint coordination should be allocated to the headquarters to support the commander’s decisions. This would be a crucial distinguishing feature from the current ad hoc approach of creating temporary JTF structures in response to specific contingencies.

Secondly, during contingencies, the PJHQ should host high-ranking liaisons dispatched from the commands of major component forces, at a ranking as high as the deputy commander level. This arrangement will help the joint commander exercise strong C2 over the subordinate forces and facilitate major component force commanders in making effective inputs to the joint commander on their operational needs on the frontlines. The most important consideration will be ensuring operational integration in the field while avoiding unnecessary duplication.

US Marine Corps Forces meet with Japanese Minister of Defense in Tokyo during the 2022 Pacific Amphibious Leaders Symposium. 17 June 2022.Source: Getty

The forward INDOPACOM option

Discussions about establishing the permanent joint headquarters for the SDF have also stimulated similar debates on reinforcing the joint functions of US forces in Japan. Currently, there is no Japan theatre joint commander in the US forces: the United States Forces Japan (USFJ) only has administrating authority, while each component force located in Japan is subordinate to the command of the service commander in Hawaii. This is a reflection of the fact that the United States has historically emphasised Japan’s geostrategic importance for hosting US forces to prepare for contingencies in the region, including in Korea, Taiwan, or Southeast Asia, rather than perceiving an imminent threat of attack on Japan’s own territory.2 Thus, for a long time there has been little need to establish a joint command structure at the Japan theatre level. However, the recent tension over the Taiwan Strait and the Chinese military’s modernisation focusing on long-range missiles as well as naval and air capabilities has changed this premise, as the security of Japanese territories has now become nearly inseparable from the security of Taiwan. This is due to the proximity of the Southwest Islands of Japan to Taiwan and shared alliance views about the increased importance of US bases in Japan in a Taiwan contingency, requiring the joint command structure of US forces in the Japan and Taiwan theatres.

However, simply elevating the USFJ Commander to the joint operational commander in the Western Pacific alone might not necessarily solve the problem. This is because the Seventh Fleet and the Third Marine Expeditionary Force (IIIMEF) have wider areas of responsibility compared with the Fifth Air Force, headed by the dual-hatted USFJ Commander, which covers the air defence of Japan. Thus, the Seventh Fleet and IIIMEF may be hesitant to make themselves subordinate to the Commander of the USFJ. Even if the ‘joint operational’ USFJ Commander is specifically appointed separately from the Fifth Air Force commander, it is still questionable to assume that the USFJ with a long-standing history and culture of administrative authority will be transformed into a joint operational command. This would also raise difficult questions regarding whether or not US forces outside Japan in the Western Pacific such as forces in Guam and Singapore, closely linked to USFJ, should be subordinate to a joint operational USFJ Commander.

For this reason, I argue that only the Indo-Pacific Command (INDOPACOM) can exert C2 over such widely dispersed US forces in the Western Pacific. Yet at the same time, the forward presence of the US joint operational command will also contribute to effective expeditionary operations to defend the region. In this regard, as Christopher Johnstone and Zack Cooper have pointed out, the INDOPACOM could deploy its standing forward command function to Japan to oversee joint operations of component forces in Japan. Having some parts of the INDOPACOM in Japan may make communication between the SDF’s PJHQ and the INDOPACOM easier. Furthermore, it may also make US component commanders in Japan who are subordinate to joint command and control more effective, because the INDOPACOM, even if it is forward deployed, would remain their superior command. Specifically, it will be suitable for distant operations near Taiwan, which would require a higher level of integration between expeditionary naval fleets and supporting air and ground-launched missile forces. On the organisational construct, whilst there may be certain practical hurdles, the appointment of the Deputy INDOPACOM Commander to the dual-hatted joint operational commander stationed in Japan with some INDOPACOM staffing would be an option for keeping the integrity of the command function of the INDOPACOM. Before and during a contingency, a forward INDOPACOM could be reinforced with additional staff.

A hybrid C2 cooperation construct

Japan’s tilt toward forward denial will also change the division of labour between Japan and the United States. Traditionally, while Japan has the “primary responsibility” to defend its territory, the United States is supposed to support and supplement such effort with offensive capabilities. This has been expressed as a so-called “shield and spear” construct. The 25-year effort since the release of the 1997 Japan-US Defense Guidelines has incrementally added additional responsibilities for Japan to support US forces, including rear area support (logistical support), asset protection, and the limited use of collective self-defence, though the basic division of labour between Japan and the United States — of supporting and being supported — has been maintained.

Such distinction has also provided a basis for the parallel C2 relationship between Japan and the United States. The 2015 Japan-US Defense Cooperation Guidelines states as one of its principles that “[s]ince the objective of the Guidelines, however, is to establish an effective framework for bilateral cooperation, the two governments are expected to reflect appropriately the results of these efforts, based on their judgment, in their specific policies and measures.” It also provides that “the two governments respectively will employ a whole-of-government approach, utilizing their respective chains-of-command, to coordinate actions through the Alliance Coordination Mechanism.” In short, the Japan-US alliance has not assumed full integration of the bilateral C2 structure in which the combined commander is appointed from US commanders like NATO and the US-ROK alliance.

In short, the Japan-US alliance has not assumed full integration of the bilateral C2 structure in which the combined commander is appointed from US commanders like NATO and the US-ROK alliance

This also seems to require an update. Blurred functional distinction between the SDF and US forces as a result of Japan’s acquisition of offensive capabilities will create chances for the SDF and US forces to cooperate in the same theatre in a manner that requires high-tempo, real-time coordination between the two parties. If so, a clear separation of the C2 structures of the SDF and US forces might cause deficiencies or problems in an operational context. This was why the Japan-US two-plus-two meeting in January 2023 committed “to exploring more effective Alliance command and control relationships to enhance interoperability and responsiveness.”

At the same time, one should be reminded of the fact that the two parties do not share all their activities under the alliance. Mutual assistance in the case of the defence of Japan is the core of the alliance, but the scope of the activities of US forces in the event of an attack on the Japanese homeland would go beyond the defence of Japan. Although Japan will likely support such activities by permitting the use of bases in Japan and by other non-treaty cooperation provided in the guidelines, and notwithstanding the fact that the two parties’ missions are increasingly aligned, there would be certain political and legal limitations on what the SDF could do. In addition, it would be politically difficult to make an arrangement in which the US commander takes the operational command of the whole SDF in the case of the defence of Japanese territory where the lives of Japanese citizens are concerned. For these reasons, it would be unrealistic to have a fully integrated C2 between US forces and the whole SDF.

However, this does not necessarily mean that the two parties should maintain the conventional separate C2 structures, especially given the shift in Japan’s force posture and the current regional strategic environment. C2 integration is not necessarily a matter of all or nothing: there should be intermediate options. On this point, the basic relationship between the ‘supporting’ and the ‘supported’ provided in the guidelines will be a good starting point to study how to deepen bilateral C2 cooperation. To move this relationship forward, I argue that while Japan and the United States should keep the basic policy of maintaining separate commanders over their respective forces, a hybrid C2 cooperation principle could be arranged in which the supported party takes operational control (OPCON) over the supporting party depending on the circumstances.

Based on this arrangement, it would be assumed that the SDF commander takes OPCON over some US forces in the defensive operations within its territories and in the area surrounding Japan, whereas US forces take OPCON over some SDF units or fleets in US-led expeditionary operations near the east side of Taiwan, as necessary. In the latter case, Japan might benefit from contributing certain naval fleets and stand-off missile units as fire-supporting forces to the US commander as a means of effective forward denial to defend its territory.3 The figure below describes the image of such a construct.

The outline of the Japan-US C2 arrangementSource: Supplied

The geographical areas of the two kinds of operations may overlap in certain areas, but the mission-oriented distinction between territorial defence and forward expedition/denial would be important. Close coordination between the PJHQ and US joint operational command would also be key, because the flexible nature of this arrangement may require planning, simulation, and exercises during peacetime. Utilization of the Bilateral Operations Coordination Center (BOCC), originally established as the primary bilateral operational coordination body in accordance with the 2015 guidelines, would be one option. Establishing a standing bilateral joint staff body might be another option. In any case, the core function should be standing staff coordination.

Such a hybrid C2 cooperation arrangement could strike a balance between reflecting the complex geopolitical environment in which Japan is located, and satisfying operational-technological imperatives for real-time bilateral cooperation. Japan’s forward denial posture has the potential to increase the effectiveness of its territorial defence at home as well as to contribute to strengthening deterrence in the region. Japan and the United States should seize this potential by modernising bilateral C2 cooperation with this hybrid construct.


This article was commissioned as part of the Japan-Australia-United States trilateral security study project, Assessing the implementation of Abe's National Security Strategy