Much of the equipment in use by the KPA is engineered and manufactured by the domestic defense industry. Weapons are manufactured in roughly 1,800 underground defense industry plants scattered throughout the country, most of them located in Chagang Province. The defense industry is capable of producing a full range of individual and crew-operated weapons, artillery, armored vehicles, tanks, missiles, helicopters, submarines, landing and infiltration craft and Yak-18 trainers, and may even have limited jet aircraft manufacturing capacity. According to North Korean state media, military expenditure amounted to 15.8 percent of the state budget in 2010. The U.S. State Department has estimated that North Korea's military spending averaged 23% of its GDP from 2004 to 2014, the highest level in the world. North Korea successfully tested a new type of submarine-launched ballistic missile on 19 October 2021.