President Barack Obama greets Matthew Barzun, the U.S. ambassador to the United Kingdom of Great Britain and Northern Ireland; U.S. Air Force Col. Angela Cadwell, the commander of the 501st Combat Support Wing; and Col. Douglas Mellars, the commander of the 422nd Air Base Group, during a visit to RAF Fairford, England, Sept. 3, 2014. After speaking with the ambassador and colonels, the president departed for Wales to attend the 2014 NATO Summit.