The club currently consists of full members France, Germany, Spain, Belgium and Luxembourg as well as eight junior partners, including Poland, who each contribute a handful of technical staff.

Eurocorps is not an EU institution. It was set up as an independent Franco-German project in 1992 to help support EU, NATO and UN operations, seeing active service in Bosnia, Kosovo and Afghanistan so far.

The organisation has strong political links to the EU, however. Its badge is a sword superimposed on a map of Europe and the EU's golden stars. A Eurocorps unit hoisted the EU flag and played the EU anthem outside the EU parliament in Strasbourg on "Europe Day" last week.

"Our decision to fully join Eurocorps comes from the conviction that Europe is becoming the second pillar of our national security alongside NATO," Polish defence minister Bogdan Klich said in Polish daily Rzeczpospolita on Thursday (15 May).

"We treat NATO as the main security pillar, but we cannot forget Europe is increasing its capabilities and this stands behind our desire to join this process."

The EU has a mixed bag of military cooperation projects under its European security and defence policy chapter, with an EU-flag peacekeeping force currently at work in Chad.

But the new Lisbon Treaty could deepen military integration with a new article that envisages "the progressive framing of a common defence policy [that] will lead to a common defence, when the European Council, acting unanimously, so decides."

"We have to start a discussion on increasing the planning and operational capabilities of the EU. We expect a serious debate will start under the French [EU] presidency," Poland's Mr Klich said.