A Sector is a shore-based operational unit of the United States Coast Guard. Each Sector is responsible for the execution of all Coast Guard missions within its Area of Responsibility (AOR) with operational support from Coast Guard Cutters and Air Stations. Sub-units of a Sector include Stations and Aids to Navigation Teams. Some Sectors also have sub-units such as Sector Field Offices and Marine Safety Units that are responsible for mission execution in part of the Sector's AOR. There are 35 sectors in nine districts and two areas.