China is currently engaged in a substantial military build-up that is unsettling her neighbours. It is widely suspected that the military build-up is in part a strategy to enforce their territorial claims over the South China Sea and its resources, notably the disputed Spratlys islands that are claimed by five countries. According to a group of former USA military leaders, China is forming a limited military force capable of rapid response and designed to protect island claims in the South China Sea as a matter of national priority. China has particularly build up its military in specific areas by improving its ability to fight a sustained sea battle with its fleet of surface warships, support vessels and submarine forces, organizing a handful of marine units for amphibious assaults and training airborne forces for rapid deployment, negotiating with Russia for the purchase of 72 advanced Su-27 attack aircraft capable of providing close air support for naval operations at extended range.