Originally published by Pacific Forum, this article is republished with permission.

While operational planners in the United States, the Republic of Korea and Japan have made historic strides institutionalizing trilateral security cooperation, the credibility of deterrence ultimately hinges on a more punishing variable: wartime sustainment.

Washington, Seoul, and Tokyo have expanded joint exercises, real-time missile warning data sharing, and regular ministerial consultations. Yet interoperability – the ability of allied systems to communicate and execute coordinated tactical actions – is not interchangeability, and neither guarantees endurance under fire.

A coalition capable of tracking an incoming hypersonic glide vehicle or ballistic missile on the opening day of hostilities may still fail if it cannot replace expended interceptors, repair battle-damaged warships, or refuel dispersed forces two months into an enduring campaign.

The fundamental dilemma is coalition logistics under national sovereignty. The three countries do not possess a combined command authority, unified stockpiles, or an integrated industrial apparatus. National authorities retain final say over the movement, maintenance, and allocation of their defense resources. An adversary seeking to fracture the trilateral alliance need not destroy every frontline combat platform; it merely needs to interdict the fragile supply chains that keep those forces armed and operational.

The tyranny of distance and precision interdiction

Northeast Asia presents a severe sustainment geography. Coalition operations spanning the Korean Peninsula, the Japanese archipelago and surrounding maritime approaches rely on concentrated nodes: deep-water ports, air depots, rail junctions and fuel bunkering sites.

Under modern anti-access and area-denial envelopes, these hubs face constant risk from long-range precision-guided munitions, submarine blockades, electronic warfare and cyber disruptions.

The operational solution cannot rely solely on extreme tactical dispersion, which dramatically inflates fuel consumption, transport requirements and coordination friction. Instead, allied planners must transition toward distributed logistics architectures characterized by redundancy, modular field repair and rapid reallocation.

What is more, to ensure continuous combat power, the coalition must eliminate single points of failure across its distribution network before hostilities commence.

Sovereign silos and munitions exhaustion

Recent global conflicts and prolonged naval engagements – such as the unprecedented burn rates of precision munitions in Ukraine and surface-to-air interceptors during Red Sea counter-drone and counter-missile operations – underscore how rapidly high-end warfare depletes magazines. Possession of advanced fifth-generation platforms is meaningless if magazines run empty within weeks.

Although the US, the ROK and Japan operate complementary platforms – including advanced stealth fighters, Aegis-equipped destroyers and Patriot missile batteries – their inventories remain largely non-interchangeable. Discrepancies in fire-control software, cryptographic standards, technical documentation and safety certifications prevent allied units from cross-loading identical ordnance.

Above all, this is a political obstacle rather than an engineering barrier. In the opening stages of a conflict, national leaders may hesitate to release scarce interceptors to an ally while facing threats to their own homeland. If ammunition transfers require ad-hoc diplomatic negotiations during an escalating crisis, the coalition trades operational velocity for bureaucratic paralysis.

Rather than chasing an unrealistic, unified stockpile, partners should establish pre-authorized national reserve pools. Governments must outline in advance which precision munitions and subcomponents can be released automatically under defined operational contingencies.

The ROK-Japan bilateral fault line

The most delicate vulnerability in this operational architecture lies in ROK-Japan bilateral relations. Trilateral momentum often relies heavily on Washington serving as a diplomatic hub, leaving direct Seoul-Tokyo operational ties brittle. Historical grievances, domestic political polarization and territorial friction over disputed islets have repeatedly spilled into national security ties. While the resumption of the General Security of Military Information Agreement restored basic intelligence sharing, structural gaps persist across several operational areas.

The most glaring gap is the total absence of a mutual logistics agreement. The ROK and Japan maintain acquisition and cross-servicing agreements with the US, and Japan has established bilateral agreements with Australia, the United Kingdom, Canada and France. However, Tokyo and Seoul have never concluded a mutual pact. Consequently, there is no direct legal framework governing reciprocal logistics transfers, refueling, ammunition supply or shared medical and depot support between the ROK Armed Forces and the Japan Self-Defense Forces.

Compounding this legal void are acute sensitivities regarding sovereignty and territorial access. Seoul’s domestic politics remain hypersensitive to any physical Japanese military presence on or near the Korean Peninsula. Current ROK policy requires explicit presidential and parliamentary authorization before Japanese ships or aircraft can enter ROK territorial waters or airspace, even for humanitarian non-combatant evacuation operations or rear-area support during a northern invasion.

Conversely, Tokyo faces constitutional constraints under its pacifist legal charter and complex statutory criteria governing survival-threatening situations before authorizing collective self-defense operations in support of peninsular contingencies.

Divergent strategic priorities further complicate bilateral cooperation. While Seoul prioritizes deterrence and defense against the immediate existential threat posed by Pyongyang, Tokyo’s security architecture is increasingly oriented toward defending its southwestern islands and deterring a Taipei contingency. If a crisis erupts in the Taiwan Strait, the ROK may resist having US Forces Korea drawn directly into conflict, while Japan would expect robust regional logistical support.

Without concrete, institutionalized solutions to these bilateral friction points, the logistical backbone of trilateral deterrence risks breaking under political strain.

Shipyard constraints and forward maintenance

Maintenance, repair, and overhaul represent another vital seam. Modern naval and aerial combat inflicts severe platform attrition. When warships or aircraft sustain combat damage, towing or flying them across the Pacific to continental American facilities guarantees their removal from the fight for months. Northeast Asia hosts premier commercial shipbuilding and aerospace sectors in South Korea and Japan, yet capitalizing on this infrastructure requires addressing statutory and regulatory hurdles.

American statutory law – specifically 10 USC 8680 – restricts the overhaul, repair, or maintenance of American naval vessels homeported in the US at foreign shipyards, subject only to narrow exceptions for voyage repairs, combat damage or short-duration corrective maintenance. Expanding foreign repair capabilities requires deeper statutory relief, streamlined security clearances for allied dry docks, and standardized technical data packages.

Forward-deployed US naval units already utilize private ROK and Japanese shipyards for maintenance but expanding this practice into pre-certified wartime battle-damage repair depots remains critical.

Reciprocal allied overhaul presents an equally pressing challenge. Just as American vessels must tap ROK and Japanese commercial yards, defense planners must resolve whether a ROK naval destroyer can legally and technically receive emergency dry-docking and repairs in Japanese ports, or if Japanese vessels can access maintenance facilities in southern Korean harbors without triggering domestic backlash.

Toward an integrated sustainment framework

Bridging these political and logistical gaps requires practical institutional mechanisms that respect national sovereignty while establishing routine operational coordination. Rather than attempting to establish an unviable supranational command, the three partners should form a standing trilateral coordination cell.

This body would coordinate cross-theater logistics visibility, match allied requests for critical components with available supplier capacity, harmonize diagnostic data for shared platforms, and manage wartime deconfliction for shared transport corridors.

In parallel, a resilient coalition must pre-delegate logistical authority through formal emergency transfer mechanisms. Policymakers should formalize emergency agreements that grant theater commanders pre-approved parameters to release specific stocks of fuel, ammunition, and critical electronics to partner forces during designated contingencies. Resolving competing allied demands through clear prioritization matrices will prevent zero-sum political maneuvering mid-crisis.

Finally, the partners must embrace autonomous resupply in contested littoral waters. Traditional theater resupply depends on large, vulnerable logistics transports that present lucrative targets within adversary missile envelopes. Incorporating uncrewed systems provides an attritable, survivable alternative.

Autonomous low-profile vessels can covertly move critical ordnance and specialized replacement assemblies across the Tsushima and Korea Straits, while heavy-lift logistics unmanned aerial systems enable rapid intra-theater transfers of avionics components and medical supplies between dispersed island outposts and frontline airfields.

Integrating autonomous platforms reduces the risk to crewed logistics vessels while providing responsive, dispersed distribution across contested waters.

Passing the logistics test

Conventional deterrence in the Pacific has long been measured by visible, high-end assets: carrier strike groups, fifth-generation fighter sweeps and advanced missile batteries deployed on the opening day. But deterrence without logistical endurance is an empty posture. A potential aggressor will not only evaluate the initial salvo; it will assess whether the US, the ROK and Japan possess the industrial capacity, legal flexibility and political will to sustain intense combat operations through several months of sustained conflict.

Addressing the logistics test demands political candor before shots are fired. It requires dismantling statutory barriers to foreign repair, establishing pre-authorized munitions transfers, and – above all – confronting the bilateral sensitivities between Seoul and Tokyo that hinder genuine mutual sustainment. By converting peacetime interoperability into wartime interchangeability, the trilateral partnership can ensure its deterrence remains credible, resilient, and unbreakable.

Colonel  Christopher Lee (christopher.s.lee.mil@army.mil) is a US Army foreign area officer specializing in the Pacific region. He holds an undergraduate degree from the United States Military Academy and graduate degrees from Columbia University and UCLA.