The European Union needs a military headquarters to work towards a common military force, the Commission president has told MEPs in Strasbourg.
Jean-Claude Juncker said the lack of a "permanent structure" resulted in money being wasted on missions.
Part of his annual state of the union address was devoted to the UK's unexpected vote to leave the EU.
He insisted that the bloc was not at risk and urged Brexit negotiations to take place as quickly as possible.
Mr Juncker warned that the UK could not expect selective "a la carte" access to the internal market without accepting free movement of people.
The single market has dominated the Brexit debate in the UK. Prime Minister Theresa May distanced herself from remarks by Brexit minister David Davis when he said remaining in the single market would be "very improbable" if it meant giving up control of British borders.