Pesco aims to make member countries’ militaries much more integrated with each other | Klaus-Dietmar Gabbert/AFP via Getty Images UK and US will be allowed to join some EU military projects Under a compromise between EU member countries, outsiders will only have access on a case-by-case basis.

The EU's joint military pact will be open to countries outside the bloc, such as the U.S. and U.K., after Brexit, but only on a case-by-case basis, according to a confidential document seen by POLITICO.

The piecemeal solution represents a compromise between countries enthusiastic for outside involvement in EU military projects and those worried that opening up the pact would give outsiders the chance to grab lucrative defense contracts.

Permanent structured cooperation, or Pesco, aims to make member countries’ militaries much more integrated with each other. It was launched last year to great fanfare in Brussels, with EU foreign policy chief Federica Mogherini calling it a "historic day for European defense.”

Apart from helping to make the EU more self-reliant when it comes to defense, the aim is also to improve competitiveness and enhance innovation across the Continent's defense industry. The Commission has proposed a €13 billion European Defense Fund, in part to fund Pesco projects.

But the tricky question of whether and how much to involve allies outside the bloc has remained unresolved.

“We were too divided. This is the only solution" — Senior EU diplomat

In May, a group of countries led by the Netherlands, Belgium and Luxembourg presented a document pushing for Pesco to be opened up to outsiders. But others, like France, were concerned that opening the door to U.S and U.K. defense companies would deny EU27 industries lucrative defense work, diplomats said. Austria and Greece were also concerned that the EU would have to offer Turkey the same arrangement.

A 5-page working paper, prepared by Mogherini's External Action Service and sent to the Politico-Military Group (PMG), a committee of Council officials representing national capitals, proposes a compromise. Dated September 18, it summarizes a series of recommendations “on the general conditions for exceptional third state participation in Pesco projects” that were agreed by the PMG on September 12.

It states that countries outside the EU “will require a case-by-case consideration as the implications of this general condition will be different depending on the specificities of a project,” meaning no blanket acceptance of the U.K. or U.S. into the pact.

It adds that the participation of a non-EU country “should not lead to dependencies that would potentially hamper or block the (joint) usability or operational deployment of the capability developed in an individual project." And it stipulates that “the invited third state should provide substantial added value to achieving the objectives of the individual project (contributing with resources or expertise)."

There is also a requirement for any non-EU state involved in Pesco to "share EU values." A senior diplomat said that phrase was added specifically to allow for the exclusion of Turkey, which is a member of NATO but where the increasingly autocratic rule of President Recep Tayyip Erdoğan has caused concern in Brussels.

The Council's final decision on involving countries outside the EU is not expected until next month, but such has been the difficulty to agree on the PMG's compromise formula, it is not expected to change substantially, according to two senior EU diplomats.

“We were too divided. This is the only solution,” said one.

Under Pesco, each project usually has one lead country with others joining it. Seventeen Pesco projects have already been agreed, with another 33 proposed. It will be up to countries participating in each individual project to decide which non-EU country to invite, if any, according to the working paper.

“It is first for the project members in an individual project to consider on a case-by-case basis if and to what extent they wish to invite a third State that meets these general conditions to participate,” the document reads. That decision must be unanimous and the Council “will then confirm whether the invited third state meets the general conditions.”

Two other senior EU diplomats say that there are plans to rebrand the recently established Military Planning and Conduct Capabilities (MPCC) unit as the "EU military HQ" post Brexit. That was something the U.K., a longtime opponent of greater EU defense cooperation over concerns that it would undermine NATO, had previously blocked.