In January 2024, Canadian and United States forces deployed across the Atlantic Ocean and joined NATO Allies to secure the continent’s western flank, extending to the Arctic. The move was the first phase of Steadfast Defender, the Alliance’s largest exercise since the Cold War, sending more than 90,000 troops from all 32 NATO nations to conduct combined exercises for four months. Steadfast Defender involved more than 50 ships, 80 aircraft and 1,100 combat vehicles, and tested enablement and deployment of Allied forces across all domains in the European theater.
NATO officials called Allies’ performance in Steadfast Defender “an impressive display of unity and interoperability” resulting in greater security and deterrence in the region. The Alliance defines interoperability as the ability of Allies to act together coherently, effectively and efficiently to achieve tactical, operational and strategic objectives. Interoperability enables forces, units and systems to share common doctrine, procedures and bases, and to operate together and communicate across systems. It reduces duplication and facilitates pooling of resources among Allies and partners. Interoperability also enables forces to adapt to shifting dynamics in the security environment.
“Exercise Steadfast Defender demonstrated the incredible strength of the trans-Atlantic bond between NATO Allies in Europe and those in North America,” retired U.S. Army Gen. Christopher Cavoli, then Supreme Allied Commander Europe, said in a news release after the exercise. “The highly complex military activities conducted over the course of this exercise have demonstrated that this Alliance is capable and ready to conduct our core mission of collective defense.”
NATO has worked to improve collaboration since the Alliance’s founding in 1949. Allies recognized that if they intend to fight side by side, they need to be able to share ammunition, fuel, spare parts, intelligence, battlefield tactics, standard operating procedures and radio frequencies, according to a March 2025 report from the U.S. Army War College. The benefits and necessity of being able to operate in tandem have been evident for decades, and the Alliance has established bureaucratic structures, policies and guidelines designed to achieve interoperability. Today, interoperability remains crucial, as military personnel rely on proven systems working together “to allow them to focus on planning and executing operations across all war-fighting functions, domains and echelons,” according to the paper.
NATO identifies four main dimensions where interoperability supports the Alliance’s initiatives: technical (hardware, equipment, armaments and systems); procedural (doctrines and processes); human (terminology and training); and information (data). As NATO addresses multiple threats across all domains, achieving and maintaining the necessary level of interoperability is increasingly important but often challenging, as Allies and partners work to combine their capabilities while addressing concerns related to data security, technology integration, and language and cultural barriers. This “360-degree” threat perspective, adopted by NATO in its 2022 Strategic Concept, aims to ensure the Alliance is prepared for transnational security threats in today’s geopolitical environment.
“Russia’s full-scale invasion of Ukraine in 2022 and China’s rapidly growing military capabilities have highlighted how threats in one region can quickly impact security elsewhere,” Simon Hutagalung, retired diplomat from the Indonesian Foreign Ministry, said in a May 2025 Eurasia Review report. “NATO’s evolution into a global security organization addresses 21st-century challenges such as strategic competition, hybrid warfare and terrorism. Its long-term effectiveness depends on creating consensus regarding geographic partnerships and defining burden-sharing among member states.”
Interoperability is key to NATO achieving this goal, Hutagalung said, by ensuring the Alliance’s readiness as it faces multiple strategic competitors and technological upheaval. “NATO needs to enhance its partnership toolkit by shifting towards flexible, mission-oriented coalitions that can swiftly mobilize against emerging threats while ensuring interoperability.”
Reembracing collective deterrence
Collective defense has long been NATO’s cornerstone. After the Cold War, however, the Alliance turned its focus away from strategic competition to interstate threats such as terrorism and natural disaster response. That changed with Russia’s invasions of Georgia in 2008, Ukraine’s Crimean Peninsula in 2014 and the full-scale invasion of Ukraine in 2022. The Chinese Communist Party’s increasingly aggressive actions and weapons development also have raised concerns over security and preserving a stable and open international system.
As NATO reembraces collective defense, leaders are addressing the need to ensure Allies’ systems and practices will operate together effectively to face emerging threats. Achieving full interoperability brings a range of challenges. Each member nation has its own history, culture and military capabilities. Adding to the challenge is the changing nature of battle, including the incorporation of automation, artificial intelligence and gray-zone activities such as information warfare and lawfare.
Despite pursuing interoperability for decades, NATO Allies struggle to measure it, assess it, and build upon it fully and accurately, according to the authors of “Measuring
Interoperability Within NATO: Adapted off-the-Shelf Tool or Bespoke Solution?” a March 2025 report published by the U.S. Army War College. One obstacle to achieving interoperability is the lack of a standard format for data collection, measurement and analysis, according to the report.
“Without a standard, interpreting that data across time, nations and domains is a challenge that impairs NATO’s ability to leverage the information fully,” the authors said. “When conducting interoperability analyses, bespoke data collection and analysis takes away from time and resources that could be spent identifying lessons and acting upon them.”
Other hurdles to interoperability include identification and agreement on technical requirements and application functionality of working groups, communication and procurement issues among nations, Frank Gubbels, NATO Command and Control (C2) Center of Excellence (COE) section head, said in a 2023 paper. This can have a profound impact on C2, he said.
“At the operational level where our COE mainly assesses during major exercises, the gaps and issues regarding operating together in NATO become apparent,” Gubbels said.
Technology is the most challenging area in which to attain interoperability, according to an Army War College Carlisle Scholars report, because teams and countries have different weapons systems and vehicles. Data may not be recognizable or usable by another country. Maintaining secure voice and data communications can be a challenge, as well as sustainment and logistics.
Procedural interoperability is crucial to clearly understand authority, processes and terminology that teams need to work together. “If different Allies have different expectations of who can authorize or disallow a military strike, an Allied operation could be either inappropriately blocked or improperly authorized,” the authors of the Army War College report said. “Similarly, if Dutch forces based in Rotterdam follow different procedures for loading, securing and transporting military equipment headed east by rail to reinforce Allied defenses, Polish forces off-loading the equipment could experience inefficiencies, confusion or injury.”
NATO has identified three levels of interoperability, ranging from 0 (not at all interoperable) to 3 (fully integrated).
Level 3 — forces operate together effectively without technical, procedural or human barriers. This level is characterized by common networks, capabilities, procedures and language.
Level 2 — exists when forces are compatible and operate together without prohibitive technical, procedural or human barriers. It is characterized by similar or complementary processes and procedures.
Level 1 — forces are “deconflicted” and operate in the same operational area in pursuit of a common goal but with limited interaction due to prohibitive technical, procedural or human barriers.
At Level 0 — forces have no demonstrated interoperability and must operate independently from each other.
Closing interoperability gaps
To address interoperability challenges, NATO in 2012 launched the Connected Forces Initiative (CFI) to increase Alliance interoperability through three lines of effort: training and education, exercises, and use of technology. A key component of CFI is Federated Mission Networking (FMN), which aims to support command and control and decision-making during operations through improved information sharing with the standards and capabilities that exist at the time of need. The all-inclusive structure of FMN’s framework is governed and managed. It provides a permanent ongoing foundation with processes, plans, templates, enterprise architectures, capability components and tools needed to prepare, develop, deploy, operate, evolve and terminate mission networks.
In May 2025, NATO released a new data strategy, setting a 2030 target date to “facilitate the exploitation of curated, quality data between Allies, the NATO enterprise and their respective communities of interest.”
“The Data Strategy for the Alliance aims to accelerate NATO’s transition into a datacentric organization, leveraging quality data for seamless interoperability and integration across all domains by providing guidance for managing NATO data and operationalizing its use for joint and multidomain operations,” NATO said in a news release.
The Alliance also regularly engages in full-scale, multidomain exercises to enhance procedural and human interoperability. In addition to Steadfast Defender, NATO conducts multidomain exercises throughout Europe and in the Arctic each year.
“As the warfighting of tomorrow becomes more complex in a multidomain environment, we need to ensure that we are in every aspect faster and better than our competitors,” German Air Force Gen. Chris Badia, then Deputy Supreme Allied Commander Transformation, said during a January 2024 NATO news conference. “This goes with nations’ transformation and this is a perpetual journey and not a one-time event. Our war transformation journey pushes boundaries, forging a collective edge in order to become better every day.”
As NATO works to sustain its long history of successful deterrence, Allies working together to embrace emerging technologies will ensure its strength continues, said Lt. Col. Jahara Matisek and James Micciche, then a U.S. Army strategist, in a February 2025 Small Wars Journal report. Strengthening interoperability in the human dimension, they added, is critical. Despite technological advancements, warfare remains at its core a human endeavor. Building trust and relationships is crucial and is achieved with sustained engagement.
“In practice, this means investing in personnel exchanges, joint training exercises and collaborative research and development initiatives,” Matisek and Micciche said. It also involves “cultivating cultural awareness and linguistic skills among military personnel to facilitate deeper understanding and more effective communication with diverse partners.”