As of mid-2014, the authors estimate that there are approximately 16,300 nuclear weapons located at some 98 sites in 14 countries. Roughly 10,000 of these weapons are in military arsenals; the remaining weapons are retired and awaiting dismantlement. Approximately 4,000 are operationally available, and some 1,800 are on high alert and ready for use on short notice. The largest concentrations of nuclear weapons reside in Russia and the United States, which possess 93 percent of the total global inventory. The United States today stores nuclear weapons at 18 sites, including 12 sites in 11 states in the United States and another six sites in five European countries. There is considerable uncertainty about the number of Russian nuclear weapons storage sites, but the authors estimate that Russia today stores nuclear weapons permanently at 40 domestic locations.