China's People's Liberation Army is the world's largest military force, with a strength of approximately 2,250,000 personnel (about 0.18% of the country's population). The PLA comprises five main service branches, consisting of the PLA Ground Force, PLA Navy (PLAN), PLA Air Force (PLAAF), Second Artillery Corps (strategic missile force), and the PLA Reserve Force. Military service is compulsory, in theory, for all men who attain the age of 18; women may register for duty in the medical, veterinary, and other technical services at ages as young as 14. However, a draft in China has never been enforced due to large numbers of volunteers from China's huge population. Demobilized servicemen are carried in a ready reserve, which is reinforced by a standby reserve of veterans and by the militia.