I. Introduction
“As the EU pushes forward with its climate agenda, the strategic consequences for defence are being overlooked”, Nestoras (2025) warned in an article on European military readiness. Other commentators similarly predict and fear that EU environmental objectives will undermine military preparedness (Bridges, 2025; Clark & Williams, 2021; Cousins, 2025; Furfari, 2025, 2026; Stuttaford, 2026; Waltz, 2023). Their message is stark: war has returned to Europe’s borders, so Europe must be prepared. Although not an established academic consensus, these arguments capture a prominent concern across current defence debates: environmental objectives may constrain military choices and weaken defence effectiveness.
However, this need not be the case. Academic research argues that this assumption overlooks the possibility that environmental and military interests could converge (Depledge, 2023; Depledge & Santos, 2025; Samaras et al., 2019). Military operations depend on reliable energy access, but the supply and management of energy impose logistical demands and operational vulnerabilities. So, using energy more efficiently can reduce environmental impact, ease pressure on military supply systems and potentially strengthen operational resilience. Incorporating environmental objectives into defence may therefore create both operational opportunities and constraints.
Within the EU, this relationship also has an interoperability dimension. Russia’s war against Ukraine and Europe’s deteriorating security environment have reinforced the importance of defence cooperation among Member States. When preparing for multinational operations, national armed forces require compatible infrastructure and logistical arrangements. It is here that environmental measures may acquire an interoperability function. When developed cooperatively, they could encourage precisely such common systems and procedures. This article therefore asks: Can the pursuit of EU environmental objectives in the defence sector support interoperability among Member States without compromising defence effectiveness?
Of course, environmental objectives encompass too many measures to examine fully in a single article. This article, therefore, focuses on military energy efficiency as one concrete example. It analyses the Smart Energy Camps demonstrator in Mali, the multinational INDY project and PESCO’s Energy Operational Function.
It argues that energy efficiency shows how environmental objectives could support interoperability. Nevertheless, these initiatives demonstrate a pathway towards interoperability rather than its widespread achievement across the EU.
II. Environmental objectives, defence effectiveness and interoperability
This section establishes how the initiatives examined below will be assessed. It explains why military energy efficiency can be treated as an environmental objective and what it would mean for such a measure not to compromise defence effectiveness. It then defines interoperability in relation to military energy use. On this basis, the section identifies two possible links: energy efficiency may reduce operational logistics, while cooperative development may encourage compatible systems and shared practices.
Environmental objectives in defence include measures intended both to reduce the environmental harm caused by military activities and to prepare armed forces for changing environmental conditions (European Defence Agency, n.d.; NATO, 2024). The relationship between defence and the environment is therefore complex (Koutouzi, 2023). Armed forces contribute to environmental degradation through their operations and resource consumption, while also implementing measures to limit their environmental impact and adapt to environmental change (Vogler, 2024; Zerey & Glas, 2026). Within the EU, these broad objectives are increasingly being incorporated into defence policy (European Commission and High Representative, 2023; European Defence Agency, n.d.).
Within this broad agenda, this article focuses on military energy efficiency for three reasons. First, it represents a concrete environmental objective: reducing the energy required to perform military functions can lower resource consumption and environmental impact (Dvořák & Štoller, 2022; Energy Security, 2024). Second, it is directly relevant to defence effectiveness because energy use affects logistical requirements and operational vulnerability and resilience. Third, several EU initiatives involve cooperation on energy-efficient military infrastructure, which provides examples for this research.
Defence effectiveness can have a broad meaning. Biddle (2017) defines military effectiveness as the ability to produce favourable military outcomes. Since this article examines energy-efficiency measures in deployable camps, it focuses on the operational aspect that those measures can directly affect: the ability of armed forces to carry out and sustain their missions under difficult conditions, including when access to energy is uncertain (European Defence Agency, 2016; NATO, 2024). This focus reflects the concern in EU defence policy and academic literature that environmental change should be pursued without weakening military capability.
Therefore, the relevant test is not whether energy efficiency increases military power in every aspect, but whether it can be introduced without preventing armed forces from fulfilling their operational tasks and whether it can help sustain those tasks by reducing logistical dependence.
Interoperability generally refers to the ability of national armed forces to operate together in pursuit of shared objectives (NATO, 2023). Since the concept covers many areas of military activity, this article applies it specifically to energy use in multinational operations. It concerns whether EU Member States can use compatible energy infrastructure and coordinate their energy-related logistics. It also requires sufficiently aligned procedures for planning and managing energy. This leads to a distinction between technical and procedural interoperability. Technical interoperability covers whether equipment supplied by different Member States can connect and work together. Procedural interoperability concerns whether their armed forces approach energy planning in compatible ways.
Energy efficiency matters to defence effectiveness because deployed military infrastructure depends on reliable energy. Supplying this energy can create a logistical burden, while transporting fuel into operational areas may expose supply lines to disruption (Hobhouse, 2025). By reducing the energy required to perform the same military functions, efficiency can lower environmental impact and reduce dependence on deliveries (Samaras et al., 2019; European Commission and High Representative, 2023). However, easing the logistical burden does not automatically lead to interoperability.
The link to interoperability appears when Member States develop energy-efficient solutions together. Energy efficiency alone does not ensure that national systems can function together. A camp may use efficient generators or battery storage, while remaining incompatible with equipment supplied by another Member State. This can happen when systems use different technical interfaces or are designed according to different operational assumptions.
The European Defence Agency, for instance, notes that agreeing on standards during capability development and procurement can support harmonisation and prevent incompatible national equipment (European Defence Agency, n.d.). Cooperation during research and development enables Member States to identify shared requirements before making national procurement decisions. When these requirements lead to common interfaces, equipment supplied by different countries may be combined within the same multinational camp. Technical interoperability does not require countries to buy identical systems, but their equipment must connect and function together safely.
Procedural interoperability likewise depends on compatible approaches to energy planning (NATO, 2023). An environmental objective can therefore provide a practical area around which national requirements and practices begin to converge. In this way, this cooperation lays the foundation for interoperability.
About the author
Elise Ceenaeme is a research trainee at Finabel.