CJEF: A Solution in Search of a Problem?

Chance for a reset: French President Emmanuel Macron with UK Prime Minister Rishi Sunak in November 2022. Image: Number 10 / Flickr / CC BY-NC-ND 2.0

As the leaders of the UK and France meet in Paris, what are the prospects for future military cooperation through the Combined Joint Expeditionary Force?

Prime Minister Rishi Sunak and President Emmanuel Macron are meeting today for a Franco-British Summit focusing on security, energy and immigration. Once relatively regular events, it is symptomatic of the challenges in the relationship between two of Europe’s leading military powers that this is the first such summit since January 2018, under (then) Prime Minister Theresa May.

While the summit is not directly related to the recent improvements in the relationship with the EU that resulted in the Windsor Framework revisions to the Northern Ireland Protocol, the more measured tone taken by the Sunak government towards the EU may make conversations between the UK and France easier. This is helpful as it is likely that there will be political pressure to show progress in deepening Franco-British cooperation.

Defence cooperation has traditionally been a politically ‘safe’ space for this, largely because it remained a matter where states retained primacy. And the development of the Petersberg Tasks (1992), the Saint-Malo Declaration (1998) and Lancaster House Treaties (2010) among others, occur when the UK was keen to bolster its credentials as a European state even while other factors were leading in opposite directions. The Petersberg Tasks (grounds for the Western European Union Council to deploy military units) were agreed at a time when the UK sought opt-outs from parts of the Maastricht Treaty on European Union. The Saint-Malo Declaration happened at the time the five economic tests set out by the then Chancellor Gordon Brown kept the UK from accepting the Euro. And the Lancaster House Treaties occurred shortly after the Coalition government, under then Prime Minister David Cameron, came to power, with very obvious tensions within his party about the UK’s relationship with the EU.

In many respects, the Combined Joint Expeditionary Force (CJEF), created as part of the Defence and Security Cooperation Treaty signed at Lancaster House in 2010 by President Nicolas Sarkozy and Prime Minister David Cameron, appears like a military solution to a political problem rather than a response to a military need. The CJEF is not explicitly enshrined in the treaty, although it flows from it, and the treaty makes clear (Art.5(1)) that decisions on deploying and employing forces remain a national responsibility. So, while the CJEF is a totemic symbol for Lancaster House, the problem with totems is that they become ritualistic, fixed points around which people orbit, even if over time the rationale behind them fades.

While the UK and France both have historic and contemporary interests well beyond Europe, it is difficult to see where they overlap sufficiently to deploy military forces at the top end of the CJEF

Arguably, the CJEF is a child of a different time, one where expeditionary wars of choice dominated thinking. Today, with the return of large-scale war in Europe, and concerns about peer adversaries, the size of force for which full operating capability was declared in November 2020 seems inadequate. Conflict in Europe should be a task for NATO forces operating en masse, and, with the NATO Strategic Concept and Deterrence and Defence of the Euro-Atlantic Area (DDA) Concept, the allocation of regional responsibilities with Europe supersedes any CJEF role on the European continent and necessitates corps-level capabilities (40,000–80,000 troops). And it is far too small in terms of land forces for any meaningful impact in a US–China conflict in the Indo-Pacific, which for both the UK and France is likely to be more of a maritime and air contribution to a wider US force. Beyond warfighting, more opportunity exists for the CJEF outside Europe, but that requires mutual agreement of the parties; the CJEF is not a standing force. It must be pulled together, ad hoc, for crises, which requires both states to agree to the mission and force requirements. While the UK and France both have historic and contemporary interests well beyond Europe, it is difficult to see where they overlap sufficiently to deploy military forces at the top end of the CJEF.

Where the need for such a force is overwhelming and of sufficient importance to both countries, a decision to deploy the CJEF is made easier, but then raises questions about whether the CJEF’s limited scale represents a viable military solution, at least in the land domain. Humanitarian assistance and disaster relief missions are, perhaps, exceptions, but require forces at high readiness, something that non-constituted multinational (or bilateral) forces may find difficult to achieve if political agreements are needed. The current CJEF planning assumptions sit uncomfortably between two stools. Its size might make sense for counterinsurgency missions, such as in Mali, but these tend to be enduring commitments that the CJEF would struggle to meet, while single-deployment land missions are likely to be ill-suited to the size of force available under the CJEF.

A disappointing outcome from the summit would be one where the CJEF is seen again as a political tool rather than as a military instrument, and excuses are found for deploying it merely because it has achieved its full operating capability. That it has not yet been activated and deployed is not a weakness; the failing would be to feel pressured into deploying it in an inappropriate way that prioritises political need over military utility. And if there is no military problem to which the CJEF is a solution in its current form, that itself is instructive.

However, the idea of a combined, joint Franco-British military capability has value. In the maritime and air domains, the opportunities are easier to see as naval and air forces are more easily able to operate together, and carry a lower political risk than deploying forces on the ground into conflict zones. And there are good examples of where the UK and France have cooperated in both maritime and air operations, even if not badged as CJEF. In 2018, allied to the last summit, the Ministry of Defence published details of military cooperation (and equipment cooperation), and this has continued, military to military, despite the difficult political environment. In 2021, RAF tankers supported French military operations in Djibouti, and RAF Chinooks continued supporting French operations in Mali before that mission ended in 2021. And there have been numerous exercises and deployments between UK and French naval forces including their aircraft carriers coming together on Exercise Gallic Strike in 2021.

Rather than look for problems to fit the CJEF ‘solution’, the summit should start from the military need and adapt the CJEF to fit

Beyond looking at combining existing force elements, value would arise from considering the CJEF as a Combined Joint Experimentation Force: a standing unit that seeks to experiment with new technologies, concepts and doctrine. And the conflict in Ukraine is exposing areas of weakness in the armed forces of both states that need addressing, such as counter-uncrewed air systems, agile command and control and industrial capacity, among others. Giving some of these tasks to French and British experimentation units as shared problems could offer significant benefits, in both the short and long terms. With two states participating, the costs of research and development and experimentation would be shared, able to use both states’ training facilities, engage defence industry in a way that might lead to greater industrial cooperation and joint procurement, and harness the talent in the two countries’ militaries and defence industries. As importantly, it would bring a diversity of views to problem solving in a way impossible for a single state.

Rather than look for problems to fit the CJEF ‘solution’, the summit should start from the military need and adapt the CJEF to fit, avoiding the temptation to address political challenges with a military formation ill-suited to the task. Allowing the British Army to focus on the Joint Expeditionary Force – a group of states within the right region of NATO for the UK’s contribution to the DDA – and realigning the CJEF towards experimentation and emphasising maritime and air cooperation beyond NATO’s borders could be a positive outcome from this week’s summit. This will require a delicate balancing act, especially for the hard-pressed Royal Navy and Royal Air Force, which also need to ensure their interoperability with partners in the Joint Expeditionary Force for the same reasons of European security and consistency with the NATO DDA. The CJEF remains an important vehicle for Franco-British cooperation, but realising its military value requires a change in emphasis.

The views expressed in this Commentary are the author’s, and do not represent those of RUSI or any other institution.

Have an idea for a Commentary you’d like to write for us? Send a short pitch to commentaries@rusi.org and we’ll get back to you if it fits into our research interests. Full guidelines for contributors can be found here.


Paul O’Neill

Senior Research Fellow

Military Sciences

View profile


Explore our related content