Strengthening Legal Interoperability

The Urgent Need to Sustain Mil-to-Mil Legal Engagements Across NATO

By Colonel Matthew A. Kopetski and Lieutenant Colonel Grzegorz Janiszewski, Polish Army

Article published on: May 1, 2026 in the 2026 Issue 1 of Army Lawyer

Read Time: < 15 mins

Military personnel from Romania, the United States, France, and the Republic of Moldova gather during the Romanian Land Forces and the United States’ 2024 multinational conference on international and operational law in Sinaia, Romania. (Photo courtesy of COL Kopetski)

Scene Setter

On 26 November 1941, six Japanese aircraft carriers departed from the Kuril Islands and began their voyage to Hawaii.¹ The flotilla arrived about a week later, having completed their voyage undetected by American patrols.² In the early morning of 7 December, the carrier-based aircraft took off and launched their attack on the U.S. Naval Base at Pearl Harbor.³ Although most Americans are familiar with this “date which will live in infamy,"⁴ not as many consider the importance of the attack from a military-technology perspective, as it marked the end of the era in naval warfare dominated by the battleship.⁵ In addition, the Japanese military industrial base deserves significant credit for developing shallow water torpedoes that enabled the tactical success of this mission.⁶

Those considerations aside, the important questions that we as legal professionals should consider include, “At which point along this operation’s timeline could the United States have invoked its inherent right of self-defense under international law to stop this attack?” Another pertinent question one may ask is, “To what extent does technological capability shape the legal answer to this question?”

In 1972, President Nixon authorized Operation Linebacker I, an aerial bombing campaign against North Vietnam.⁷ As part of this campaign, on 10 June, American F-4s struck the Lang Chi hydroelectric facility located approximately sixty miles up the Red River Valley from Hanoi.⁸ The Soviet Union-built, 122,500-watt installation had the capacity to supply up to 75 percent of the electricity for Hanoi’s industrial and defense needs.⁹

Attendees gather at the 9th African Accountability Colloquium in Cotonou, Benin. The colloquium was co-hosted by the Benin Defense Force and U.S. Africa Command. Commanders and legal advisers from more than thirty African countries attended this bi-annual meeting to discuss issues related to the commander/legal adviser relationship. JAs and legal professionals from U.S. Army Southern European Task Force - Africa, U.S. Africa Command, U.S. Army Europe and Africa, the National Guard Bureau, and the North Dakota National Guard all participated in this event. (Photo courtesy of COL Kopetski)

At the same time, U.S. Air Force planners estimated that breaching the dam could kill as many as 23,⁰⁰⁰ civilians.¹⁰ Upon execution, the strike force dropped 12 Mk-84 laser-guided bombs through the 50-by-100-foot roof of the main building at the base of the dam.¹¹ The strike succeeded in destroying the dam’s turbines and generators, which shut down the power plant without causing a breach.¹² Today, U.S. and North Atlantic Treaty Organization (NATO) forces plan, and, when necessary, employ precision-guided “smart munitions” as a routine component of warfare.¹³ However, the Vietnam War marked the first entry of laser-guided munitions in combat.¹⁴ Another question that we as legal professionals should ask is, “To what extent did the advent of precision-guided munitions render this attack compliant with the law of armed conflict (LOAC)?”

In September 2022, Ukraine launched the “I want to live” project.¹⁵ In simple terms, “I want to live” employs a complex system of chatbots and drones to facilitate the surrender of Russian soldiers to the Ukrainian armed forces.¹⁶ In November 2022, Ukraine released video footage of a surrendering Russian soldier being guided by a drone to waiting Ukrainian soldiers. We should examine the legal ramifications that the development of drone technology and social media has on a party to an armed conflict’s duty to accept the surrender of enemy forces.

In response to Hamas’s 7 October 2023 attack against Israel, the Israeli Defense Force used the “Gospel” and “Lavender” software systems as part of their target-identification processes.¹⁷ Gospel “compiles, fuses, and cross-references layers of information from different datasets to generate suggestions for intelligence analysts regarding objects that have the potential to qualify as a military objective."¹⁸

Lavender serves a similar function for the purpose of identifying potential members of Hamas or other armed groups.¹⁹ Both Gospel and Lavender rely on pre-existing datasets that are regularly updated. What structures must a state put in place to use software such as Gospel and Lavender to ensure that military operations relying on this information comply with LOAC?

These examples illustrate how technological advancement shapes combat operations. At the same time, they demonstrate the need for judge advocates (JAs) active in the national security law space to keep current on how the incorporation of new technologies into our weapon systems influences the legal analysis of operational planning. Additionally, JAs must remain cognizant of the fact that our Army and country do not fight alone and, therefore, we must have some understanding of the legal perspective of our allies and partners. Would a legal advisor representing Belgium, Denmark, Estonia, France, Finland, Germany, Lithuania, the Netherlands, Poland, Romania, Spain, Turkey, or Ukraine share the same interpretation as the United States? To what extent is that position shaped by the technological and military capabilities of that nation’s armed services? Working through these questions explains why JAs need to proactively and continuously work with our allied and partner nation counterparts to build and sustain a compatible shared understanding of the legal rules governing military operations.

Introduction

As the United States and its allies shake off the counterinsurgency mindset and prepare for large-scale combat operations (LSCO), JAs, along with our allied legal advisors (LEGADs), need to prepare our commanders for the legal complexities of a NATO fight on European territory. Such a fight will entail massive and complex enabling, shaping combat operations that will originate from, transit through, be conducted with, and have effects in the national territories of several allied powers, all of which will retain their sovereignty. In addition to bringing their combat power to the fight, each ally will operate under its own legal and bureaucratic regime that will shape how it employs such force.

As legal professionals, our ability to support our commanders will require us to work intimately with our legal counterparts across the combined force. Fortunately, as complex and as challenging as this task may seem, the NATO allies did it in the past and achieved victory and, if necessary, will do so again.

This article draws on many of the lessons our Corps has learned to enhance allied legal interoperability in Europe in the post 24 February 2022 environment. The authors hope that this article will motivate staff judge advocates (SJAs) and their allied counterparts to sustain these efforts to consolidate and build upon the gains achieved. To that end, this article will first clarify the concept of legal interoperability, then delve into its incorporation within legal operations, and conclude by offering a framework for its assessment.

Clarifying Legal Interoperability as a Concept

Legal Interoperability: The Legal Basis

The successful implementation of Articles 3 and 5 of the North Atlantic Treaty²⁰ demands effective legal interoperability across the alliance and those forces operating in a NATO formation. Article 3 requires that the allies “maintain and develop their individual and collective capacity to resist armed attack."²¹ In the event an armed attack against a NATO ally occurs, Article 5 demands that all allies “assist the Party or Parties so attacked by taking . . . individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force."²² The development of a collective capacity to resist an armed attack and executing that task requires continuous dialogue and training across the allied legal community on how the allies interpret LOAC and the relevant rules that shape how they operate and meet those requirements.

In particular, the allied legal corps need to discuss, identify, and test the seams of how each ally incorporates LOAC into their force structures and maximizes the effectiveness of such collective action. Not only does this ensure legal interoperability, but it also facilitates unity of effort across the allied formations, efficient resource allocation, and enhances operational effectiveness.²³ In addition, it requires a robust corps of JAs and legal advisors that train and practice with a legal interoperability mindset.

Fortunately, the U.S. Army and NATO have established statutory and regulatory frameworks that support the implementation of Articles 3 and 5 of the North Atlantic Treaty and build interoperability across the alliance. By statute, 10 U.S.C. §§ 331 and 346 both contain language explicitly supporting the enhancement of interoperability with friendly countries.²⁴ By regulation, U.S. Army Regulation (AR) 34-1, Interoperability, states that it is the Army’s policy to “develop interoperability to enhance readiness in support of U.S. national defense and strategic goals, including operating effectively with [unified action partners (UAP)] across the [range of military operations (ROMO)]."²⁵ The Army adopted AR 34-1 understanding that it “will have only days . . . to integrate with UAPs . . . . Therefore, interoperability must become a fundamental condition of how the Army plans to fight tonight and tomorrow . . . ."²⁶ Although most people look to these sources from a materiel and operational viewpoint, one should note that the broad language they utilize captures the legal domain as well.

Legal Interoperability: The Concept

The U.S. Army, to include the Judge Advocate General’s (JAG) Corps, and NATO agree that (legal) interoperability has three core components: technical, procedural, and human.²⁷ Although AR 34–1 does not define these components, NATO’s Allied Joint Doctrine 01²⁸ (AJP 01) contains some helpful definitions. AJP 01 provides the following:

• Technical Interoperability concerns systems and equipment, such as communication and information systems, and their ability to operate together.
• Procedural Interoperability is based on measures such as common doctrine, procedures and terminology.
• Human Interoperability concerns mutual trust and understanding achieved by strengthening relationships in training and on operations.²⁹

In addition, AJP-01 links its definitions to Articles 3 and 5 of the North Atlantic Treaty by stating that interoperability depends on the ability of “NATO, other political departments, agencies and, when appropriate, forces of partner nations to act together coherently, effectively and efficiently to achieve Allied tactical, operational and strategic objectives.³⁰

Recognizing the ever-growing complexity in combined military operations and the consequent need to build legal interoperability across the NATO allies, the U.S. Army Judge Advocate General’s Legal Center and School (TJAGLCS) published Multinational Legal Interoperability³¹ in 2021. The evolution in the discussion over legal interoperability caused TJAGLCS to update the publication in 2024 and change the title to Best Practices of Multinational Legal Interoperability Smartbook.³² Although this publication recognized the enduring challenge of building legal interoperability, arguably its most significant achievement is that it adapts the AR 34–1 levels of interoperability construct to the military practice of law. These are:

In 2022, the Center for Law and Military Operations (CLAMO) published the U.S.-UK Interoperability Handbook,³⁴ the first manual focusing on establishing legal interoperability with an individual ally. In 2024, CLAMO published the Tactical Legal Polish / United States Interoperability Handbook.³⁵

Incorporating Legal Interoperability into Legal Operations

“Legal interoperability begins with a handshake.” – Lieutenant General (Retired) Charles N. Pede

In 2017, NATO put forward that “[t]he effectiveness of Allied forces in peace, crisis or in conflict, depends on the ability of the forces provided to operate together coherently, effectively, and efficiently. Allied joint operations should be prepared for, planned, and conducted in a manner that makes the best use of the relative strengths and capabilities of the forces which members offer for an operation.”³⁶ In response to Russia’s 2022 invasion of Ukraine, the NATO allies’ armies have undertaken significant effort to strengthen their collective capability to fight together in a coherent, effective, and efficient manner.³⁷

NATO’s December 2022 update of Allied Joint Doctrine serves as the doctrinal underpinning of this effort. Here, NATO elevated interoperability to one of three force multipliers that enhance the Alliance’s fighting power. In the background, the legal corps of the NATO allies, including the U.S. Army’s JAG Corps, have contributed to this effort through combined participation in hundreds of training events, exercises, and conferences.³⁸

2023 through 2025 brought a high- water mark for JA-to-LEGAD dialogue. In 2022 and 2023, Romania’s Land Forces held a bilateral conference with the United States on international and operational law. In 2024, Romania expanded this conference to include participation from the United States, France, and Moldova.³⁹ The presence of two Romanian general officers at this event, which their national television covered, signified the growing importance this engagement has taken on.

In 2024 and 2025, Bulgaria held bilateral legal conferences with the United States. In 2024, at least seventeen NATO allies sent LEGADs to the first European Multinational Judge Advocate General’s Interoperability Symposium (MJIS) hosted by U.S. Army Europe & Africa (USAREUR-AF) Office of the Judge Advocate (OJA). This conference included more NATO members in 2025.

In 2023, the NATO Joint Warfare Centre held the first iteration of the “Sword of Justice” legal exercise.⁴⁰ U.S. Air Forces Europe & Africa co-hosted with Spain the second iteration of this event in 2024. In addition to these events, JAs and LEGADs from Belgium, France, Italy, Lithuania, Romania, and the United Kingdom have participated in numerous exchanges as part of tactical training events. Although each of these events included important substantive components, one cannot understate the importance these interactions had on strengthening the human component of legal interoperability.

One should note, these events did not “just happen.” They happened because of initiatives taken by one (or several) JAs and allied LEGADs who worked together to build the event. The thirty-two sovereign members of NATO each have a separate legal culture within their armed services. NATO allies lack the organizational structure and resources that we benefit from in the U.S. Army. As a result, it often falls on the Army JA to initiate the lawyer-to-lawyer contact. Initiating the contact that leads to the first handshake constitutes the most important element in building legal interoperability with an allied or coalition partner. This contact, which is usually referred to as “an engagement,” establishes the foundation of the whole relationship and frames expectations about future cooperation.

COL Jason Coats, Chief of Administrative and International Law, Office of the Chairman of the Joint Chiefs of Staff, speaks to attendees during the Romanian Land Forces and the United States’ 2024 bilateral conference on international and operational law in Sinaia, Romania. (Credit: Victor Sandu)

“Engagement” serves as the catchall term when meeting with an ally or partner LEGAD.

In general, they seek to:

• Enhance understanding of the legal, policy, and doctrinal frameworks that shape each participating ally or partner nation’s land forces;
• Enhance understanding of each ally or partner nation’s framework for applying LOAC;
• Enhance understanding of the legal, policy, and doctrinal frameworks each ally or partner nation employs to ensure compliance with established international norms governing human rights;
• Enhance understanding of the legal, policy, and doctrinal frameworks each ally or partner nation employs to protect the rule of law; and
• Enhance the ability of the parties to provide mutual support during their combined operation.

Typically, an engagement occurs in one of four formats. These are:

• Senior Leader Outreach (SLO): SLOs consist of a meeting between the SJA and their peer from the allied or partner nation. These engagements typically establish a framework and timeline for future cooperation.
• Mission Support Engagements (MSE): MSEs are operationally focused meetings typically geared toward addressing a legal/regulatory/policy-related friction points that inhibit the successful execution of a tactical exercise or operation.
• Legal Conferences and Continuing Legal Education (CLE): These events focus on exchanging information and perspective on legal topics of common interest. In addition, they usually offer networking opportunities to facilitate mil-2-mil cooperation in training and operational environments.
• Table-Top Exercise Participation (TTX): TTXs are events focused on developing the operational law skills of JAs and LEGADs assigned to tactical formations. These events typically involve a combination of classroom instruction followed by scenario presentation to facilitate issue spotting and discussion on LOAC compliance by the training audience. In 2023 and 2024, Romania’s Land Forces held TTXs attended by U.S. JAs and French LEGADs.

The most important takeaway from the above is that building legal interoperability does not just happen; it requires effort, and most often, the SJA must make legal interoperability a priority. Fortunately, that initial effort generally entails little more than sending a friendly and professional email requesting to schedule a meeting to discuss activities, resources, and interests. JAs should strive to approach these meetings from the positive perspective of, “What can we discuss and work on that will mutually benefit our commands?”

Part 3: Assessing Legal Interoperability

“Interoperability is often considered to be a desired, but unattainable, goal rather than a condition that can be quantified.”⁴¹ – Michael Leite, PE

As JAs and military professionals, we have an intrinsic desire to focus our professional energies on the pursuit of activities that seek to achieve a defined outcome. In the legal interoperability context, this characteristic translates into a natural desire to develop programs with an ally or partner that, when completed, will lead to establishing Level 3 legal integration. At the same time, we recognize that establishing full legal integration with our thirty-two NATO allies is impossible. To reconcile this tension, we should satisfy ourselves by appreciating the fact that the trans-Atlantic alliance will remain successful at deterring aggression by concerted effort among the allies to achieve Level 3 integration, but, at the same time, in the legal context, will remain satisfied by sustaining a high-degree of Level 2 legal compatibility. Of course, the challenge remains: “Who decides where our Army sits on this spectrum vis-à-vis its NATO Allies?” And, “What is the assessment criteria?”

During my service at USAREUR-AF, I have created, seen, and helped develop several tools for assessing legal interoperability. After each engagement with an allied or partner nation, the team leader would submit a trip report that documented the most important meeting outcomes. In addition to recording the key topics of discussion, the leader also suggested discussion topics at a future meeting. The purpose behind this was to recognize that our allied and partner interlocutors change positions much less frequently than we do; therefore, we wanted to solidify any gains made at one conversation and maximize the opportunity to advance issues at another meeting. During the two and a half years I served at USAREUR-AF, we built a robust repository of these engagements. Among allies with whom the USAREUR-AF OJA has steady and robust dialogue, such as Romania, these reports show an iterative progression of mutual understanding of each other’s legal approach to a range of issues, including LOAC.

COL Kopetski (left) receives a plaque from COL Sorin Chiper (right), Legal Advisor to Romania’s Chief of Defense, commemorating the Romanian Land Forces and the United States’ 2024 bilateral conference on international and operational law in Sinaia, Romania. (Photo courtesy of COL Kopetski)

More recently, OJA and its subordinate units have begun to create “legal interoperability matrices” during the planning phases of combined exercises. Here, the National Security Law Division hosts regular planning calls with U.S., allied, and NATO counterparts to discuss aspects in the planning documents that contain legal issues. The legal office of each formation participating in the exercise participates in these calls and has the opportunity to articulate its legal position with respect to those issues. Also, they may raise other issues they have identified. These discussions have removed a significant amount of friction that, if left undiscovered until the actual event, could have hampered the achievement of multiple training objectives. Furthermore, as a result of OJA’s continuous pursuit of legal interoperability, USAREUR-AF has become much more comfortable integrating into NATO command structures.

Conclusion

The rapid pace of technological innovation and its direct impact on LSCO demands that JAs continuously create and seek opportunities to work with their NATO and allied counterparts to sustain an operationally comfortable level of legal interoperability.

The handshake is the most important tool in achieving this, but such encounters mark the beginning of cooperative engagement. JAs and their NATO counterparts should also explore exercises and other projects described above. Joint exercises are particularly important, as they allow JAs and LEGADs not only to test the differences between legal systems in practice and seek ways to resolve them, but also to solidify personal contacts.

The continued development and refinement of tactical interoperability manuals, both at the NATO level as a whole and for individual countries, would also be of practical help. This would greatly facilitate the work of JAs and LEGADs, especially those who have not had much experience in working with allied counterparts or operating in forward areas. It is also important to continuously assess the level of interoperability, draw conclusions in this regard, and implement them in practice. Over the course of several years, these activities will raise legal interoperability to a level that allows for conflict-free and smooth cooperation between the armed forces of different allied countries on legal issues. TAL

Notes