Turkey has the second-largest standing military force in NATO, after the US Armed Forces, with an estimated strength of 495,000 deployable forces, according to a 2011 NATO estimate. Turkey is one of five NATO member states which are part of the nuclear sharing policy of the alliance, together with Belgium, Germany, Italy, and the Netherlands. A total of 90 B61 nuclear bombs are hosted at the Incirlik Air Base, 40 of which are allocated for use by the Turkish Air Force in case of a nuclear conflict, but their use requires the approval of NATO.