Air Transport Agreement. Several U.S. carriers already have third-party code sharing agreements with Vietnam Airlines. Direct flights between Ho Chi Minh City and San Francisco began in December 2004. Vietnam and the United States also signed a bilateral Maritime Agreement in March 2007 that opened the maritime transport and services industry of Vietnam to U.S. firms. In 2011 the U.S. banks agreed to invest $1.5 billion in Vietnamese infrastructure. Military According to the Council on Foreign Relations, Vietnam's defense policy is based on the "Four 'No's" principle: no military alliances, no foreign troops stationed on Vietnamese soil, no partnering with a foreign power to combat another, and no force or threatening to use force in international relations. This was historically "Three 'No's"; however, the fourth, denouncing the use of force, was added in the December 2019 "National Defense White Paper", which also stated that Vietnam is willing to allow ships from other countries to dock at its ports. Cooperation between the United States and Vietnam in other areas, such as defense, nonproliferation, counterterrorism, and law enforcement, is expanding steadily. The territorial disputes in the South China Sea with China, which has become more assertive in its territorial claims, has also gradually strengthened relations between Vietnam, the U.S., and other Chinese rivals, including India and fellow ASEAN member and U.S. ally the Philippines. The U.S. favors an open South China Sea for its larger Indo-Pacific strategy and because Chinese territorial claims in the region threaten the security and prosperity of its key regional allies. With Vietnam's historically complex relationship with China that included past territorial disputes, Vietnam feels that Chinese claims and actions in the South China Sea threaten its sovereignty and territorial integrity. In this regard, American and Vietnamese security interests align as they oppose Chinese in the South China Sea. Vietnam hosted visits by five U.S. Navy vessels in 2007, including a port call to Da Nang by the amphibious assault ship carrying a multinational contingent of medical and engineering personnel. In June 2007, Vietnamese observers took part for the first time in the multinational naval exercise Cooperation Afloat Readiness and Training (CARAT), organized by the U.S. Navy. Vietnamese Prime Minister Nguyễn Tấn Dũng stated that the country is in the final stages of preparation to take part in international peacekeeping, as part of its contribution as a new member of the United Nations Security Council. When asked about