The Aerospace & Defense industry represents the production, sale, and service of commercial aircraft, as well as a source of military weapons and systems designed to operate on land, sea, and air. The production of space vehicles and satellites are also in this sector. Aerospace’s target market involves the production of commercial aircraft including commercial airlines, while the defense market provides military weapons and systems such as arms and ammunition, missiles, satellites, helicopter drones, tanks, ships, and other marine vessels, as well as their unmanned counterparts. Often the defense market is measured by military spending by country.