The European Union (EU) does not maintain its own military force and thus relies on the capabilities of each of its members should the worst come to pass. Europe is still militarily protected by the NATO alliance to an extent as twenty-two EU members are also NATO supporters / contributors. Regardless, the EU has on call (at least theoretically) over 1.5 million personnel, nearly 7,700 tanks, 2,450 aircraft (including helicopters), and nearly 550 warships and submarines.
There are a total of (24) countries of the European Union represented in the GFP database. While there are officially twenty-eight total EU members, the Republic of Cyprus, Ireland, Luxembourg and Malta are not included in this list due to unmet conditions and minimums.
UPDATE: Due to the "BREXIT" vote results which sought to take the United Kingdom out of the European Union, this list will be updated once the motion becomes official for both sides.
Sources: CIA.gov, CIA World Factbook, wikipedia.com, public domain print and media sources and user contributions. Some values may be estimated when official sources are lacking.