Wings responsible for an air base also have other dependent groups such as a mission support group (security, communications, logistics support, mission support, and civil engineering squadrons) and a medical group. The dependent group commanders are considered to be in command billets, but they function like staff officers (the A3/S-3/G-3/J3 or the A4/S-4/G-4/J4) in other organizations. Independent groups are effectively small wings with both flying and maintenance squadrons. USAF groups are usually commanded by officers in the grade of OF-5 (US pay grade O-6), i.e., a full colonel. Wings are also usually commanded by officers in the grade of OF-5, but these are typically more senior colonels by virtue of time in grade and/or date of rank. Some USAF wings are also commanded by officers in the grade of OF-6 (US pay grade O-7), i.e., a brigadier general.