In the United States Air Force, a wing is a larger unit that is normally subordinate to a Numbered Air Force. Most USAF wings are commanded by a Colonel, but some are commanded by Brigadier Generals. USAF wings are structured to fulfill a mission and contain a headquarters and four groups: an operations group, a maintenance group, a medical group and a mission support group. The 155th Air Refueling Wing is located in Lincoln, Nebraska. These groups support various missions assigned to the 155th Air Refueling Wing both locally and abroad.