a result of continuing effective defense investment due to Japan's economic development and an end to the Cold War, the JMSDF became the world's fourth largest navy by total tonnage by 2000. Japan has the eighth largest Exclusive Economic Zone (EEZ) in the world, and the JMSDF is responsible for protecting this large area. As an island nation, dependent on maritime trade for the majority of its resources, including food and raw materials, maritime operations are a very important aspect of Japanese defense policy. The JMSDF is known in particular for its anti-submarine warfare and minesweeping capabilities. Defense planners believe the most effective approach to combating hostile submarines entails mobilizing all available weapons, including surface combatants, submarines, patrol planes, and helicopters. They are also known to operate at least fourteen listening stations all over the country that have ELINT and marine surveillance radar warning systems. Historically, the Japan Air Self-Defense Force (JASDF) has been relied on to provide air cover at sea, a role that is subordinate to the JASDF's primary mission of air defense of the home islands. Extended patrols over sea lanes are beyond the JASDF's current capabilities. The Japanese fleet's capacity to provide ship-based antiaircraft warfare protection is limited by the absence of aircraft carriers, though its destroyers and frigates equipped with the Aegis combat system provide a formidable capability in antiaircraft and antimissile warfare. These capabilities are force multipliers, allowing force projection of Japan's sizable destroyer and frigate force far from home waters, and acquiring them is contentious considering Japan's "passive" defense policy. Activities International activities Mission in the Indian Ocean Destroyers and combat support ships of Japan Maritime Self-Defense Force were dispatched to the Indian Ocean from 2001 to 2008 to participate in OEF-MIO (Operation Enduring Freedom-Maritime Interdiction Operation). Their mission is to prevent the marine transportation of illegal weapons and ammunition, and the drugs which fund terrorist activity. Since 2004, the JMSDF has provided ships of foreign forces with fuel for their ships and ship-based helicopters, as well as freshwater. This was the third time Japanese military vessels had been dispatched overseas since World War II, following the deployments of mine-sweeping units during the Korean War and the Persian Gulf War. The law enabling the mission expired on 2 November 2007, and the operation was temporarily canceled due to a veto of a new bill authorizing the mission by the opposition-controlled upper chamber of