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The Army Lawyer


A Foreign Perspective on Legal Interoperability



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With apologies to Sun Tzu,“Know your [allies] and yourself; in a hundred battles you will never be in peril.”1 Bottom line up front: no two states have identical national laws; even our understanding and application of the laws of International Humanitarian Law (IHL) (Geneva and Hague being the cornerstones) are not uniform. As judge advocates (JA) and legal advisors (LEGADs), we have a central role in identifying and understanding the relevant national positions within combined forces, the implications for the force, and advising how to minimize the operational or tactical impact, in order to ensure mission accomplishment.

What Is Legal Interoperability?

The North Atlantic Treaty Organization (NATO) and national doctrines concentrate on interoperability in terms of the ability of equipment, processes, and systems to work together. For example, the ability of a German fuel supply unit to refuel a United States (U.S.) armored fighting vehicle on deployment in Estonia, where the issue may be identified when trying to fit a 1-inch imperial hose to a 2.5-centimeter metric coupling. Enabling interoperability in this context begins with identifying an issue (different diameters) and understanding the extent of deviations involved. Identifying the differences between national positions does not automatically identify a problem. In some cases, the fact that we have a different position with respect to the relevant law does not mean that we do not reach the same conclusion. The United States may not have accepted the 1977 additional protocols to the Geneva Conventions; the impact, however, is reduced where they are regarded as customary international law. The end result is often very similar, if not the same. Standardization Agreements (STANAG) require knowledge on the part of each party to enable adjustments to ensure that they can work together. In physical matters, that may be as simple as creating a flow controller on a fuel delivery system or as complex as creating an interface that can accommodate different hose diameters to refuel multiple pieces of equipment. This has been reflected in numerous NATO STANAG over the past seventy years. There is no STANAG for the application of law within NATO. There is, however, a STANAG on IHL and Law of Armed Conflict (LOAC) training, setting out common standards to achieve and measure performance.2 In addition to this, NATO member states have adopted the extensive STANAG 2597 on NATO rules of engagement (ROE) training.

Those with experience in multinational operations, whether within the NATO alliance, bilateral alliances, or ad hoc coalitions, will appreciate the difficulty of trying to achieve the same in the legal sphere. In the same way that it is unrealistic to expect all alliance members—let alone coalition partners—to use a single brand of small arms ammunition, it is unrealistic to expect them to adopt a single interpretation of international law. That said, it is suggested that the vital ground in maximizing interoperability in the legal sphere is still in identifying and then understanding what each nation cannot, or more importantly can, do in a given operational structure or situation. It is, perhaps, relatively easy for the NATO nations to agree by consensus on the common or essential characteristics of small arms ammunition. A consensus among twenty-eight nations on use of force, defensive or offensive, is more difficult. The twenty-eight NATO nations are not all party to the same international obligations and, even in those cases where there are interpretations, are not uniform. As a consequence, the application of the law will not be uniform. As an alliance, NATO needs consensus to operate; difficult areas may, therefore, be left unresolved or unrefined.

Carl von Clausewitz (he gets everywhere) referred to frictions in war. While he may not have had the law in mind when writing On War, there are legal frictions in war. These frictions and their impacts are magnified by the addition of other states to your plan. One of the JA’s roles is to understand this and to minimize the operational impact of such friction on the commander’s plan. It is overly optimistic to suggest that the JA can entirely remove such friction. While it is unrealistic to expect the JA to have a Harry Potter wand or spell with which to remove the frictions or to know all of the applicable international law positions and the domestic laws of partner nations, it is realistic to expect them to know that allies will have differences in the legal world. Acknowledging this is the first step toward achieving legal interoperability.

Why Is Interoperability Important in the Legal Sphere?

In simple terms, no alliance or coalition commander can order a national component to execute an order that exceeds that nation’s legal authorities. It is for this reason that you should expect to see a Senior National Representative or National Contingent Commander for each nation within a multi-national operation. If your command seeks to ask a nation to go outside national law/legal interpretations, you should expect to see a “red card” on the operation.3 Put another way, there is little or no utility in developing a plan that cannot succeed because a key element is legally unachievable by the nation tasked to support or achieve it. This is not the place to recite the examples of where such situations have risen.

As JAs and LEGADs, we are the commander’s, and by extension, the staff branches’ principal advisor on what can be lawfully achieved and by whom. It is important to note that a particular legal interpretation or policy may relate to either a specific legal prohibition or to a political position; both need to be considered in order to appreciate the potential for flexibility. If national legislation specifically prohibits a change in action, it is unlikely to happen in the short term. Conversely, a policy limitation on the application of the law, for example, a specified minimum approach limit in respect to an international boundary, could be changed with appropriate planning and engagement. The latter is an area where the current operations, future operations, and legal teams need to work collaboratively to ensure that the force has the authorities that it needs on the ground. One of the products of that collaboration should be a caveats matrix. In simple terms, this is a matrix setting out formal national limitations, restrictions, constraints, or deviations (legal or policy) within the consensus framework for the operation, which do not permit a multinational commander to deploy or employ national assets fully in line with the approved operational plan (OPLAN). Particularly, limitations on or interpretation of multinational ROE may directly impact the ability of national forces to perform assigned tasks.

The identification of differences and related impacts is not just about law and policy interpretations; it also includes consideration of how we use JAs and LEGADs. When considering how the U.K. armed forces use LEGADs, it would help to consider U.K. Joint Doctrine Publication 3-46 Operations.4 This publication is aimed at both the LEGAD and the commander/staff in setting out relationships and responsibilities.

How Do We Collectively Improve Legal Interoperability?

There are two streams through which we can improve legal interoperability without becoming engaged in the complexity of altering national legislation. The two streams are (1) individual actions and (2) collective actions. The former is simple in that it requires the individual to learn about how allied or coalition partners apply law on operations. To start, there are various resources available, such as the U.K. Joint Service Manual of the Law of Armed Conflict, the German manual, and the NATO legal desk book. The NATO Allied Joint Publications (AJP) cover a wide array of inter-operational topics: AJP 3, the Conduct of Operations; AJP 5, the Operational Level Planning; and AJP 13, the Coalition Operations Handbook. In terms of developing practical knowledge, you may consider requesting to attend courses, such as the U.K. Brigade Legal Officers Course or the NATO schools at Oberammergau or Chievres (for Special Operations Forces) or the International Institute of Humanitarian Law (those already in Europe may have a logistical advantage). International exercises also provide many opportunities.

The collective element is more in the way of what can the relevant Staff Judge Advocate (SJA) do to enable the proactive subordinate to exploit opportunities for identification of issues and understanding impacts. How does a SJA respond when a subordinate presents a properly articulated request to observe an exercise, attend a school of instruction, or acquire a manual/text book? If you can’t afford to support the request ahead of time, will you be able provide support when called on to deploy at short notice?

In closing, consider the following from Major General Walter E. Piatt in 2014:

Building trust and understanding each other’s capabilities and procedures are key to coalition operations – from disaster response to full out war. . . .You don’t want to meet the team on the ground for the first time. We saw this many times in Afghanistan, where you would be meeting forces from other nations for the first time when you have a real operational demand. We’re doing that now so the relationships and trust are in place before deployment.5

One observation from personal experience is that there is no substitute for already knowing a name and face when you arrive in a foreign theatre of operations. If nothing else, they can tell you where to get a cup of coffee to help you through late night reading. TAL

The views expressed in this article are entirely and solely those of the author and do not necessarily reflect official thinking or policy either of Her Majesty’s Government or of the Ministry of Defence. This article is a reprint of a previously published version.


LtCol Larkin is currently assigned as Commander Legal, 1st (United Kingdom) Division.

Mr. Bartels is currently the Deputy Director of the Office of Legal Affairs at the NATO Supreme Headquarters Allied Powers Europe.


1. The original quote from the Art of War reads, “Know the enemy and know yourself; in a hundred battles you will never be in peril.” See Sun Tzu, The Art of War (Thomas Cleary trans., Shambhala ed. 2005).

2. Allied Training Pub., Training in the Law of Armed Conflict (20 Mar. 2013) [hereinafter STANAG 2449].

3. A “Red Card” may be described as a national commander (the Red Card Holder) highlighting an action or activity that the particular nation is unable to comply with.

4. Joint Doctrine Publication (JDP) 3-46, Legal Support to Joint Operations (3d ed. 2018).

5. See Jim Garamone, Reassurance, Interoperability Key for U.S. Army Europe, U.S. ARMY (22 Oct. 2014), https://www.army.mil/article/136479/Reassurance__interoperability_key_for_U_S__Army_Europe.