The United States has long encouraged Japan, as one of its close military allies, to build up its defensive capabilities. Despite its pacifist constitution, Japan proved a critical military ally during and after the Cold War, when its prowess in anti-submarine and mine countermeasure warfare complemented and enhanced the United States' presence in the Pacific. Focused exclusively on defense, Japan's Self-Defense Forces have deliberately eschewed offensive weaponry and forces such as nuclear submarines, fixed-wing carrier aviation, dedicated amphibious forces, large-scale airborne forces, suppression of enemy air defense capabilities, ballistic missiles or land-attack cruise missiles. Instead, Japan's military has traditionally acted as the shield to the United States' sword, providing not only a base but also protection for U.S. force projection in East Asia.