To administer these islands, the United Nations created the Trust Territory  of the Pacific Islands in 1947. It also noted that it would be unwise  to assume that the end of the Cold War has lessened the strategic  importance of Micronesia to U.S. interests. U.S. Military Operations and Facilities on Kwajalein Atoll, Republic of the Marshall Islands

The United States has maintained a military presence in the Marshall  Islands for several decades, and DOD currently conducts ballistic missile  and missile defense testing on Kwajalein Atoll. Use of Primary Compact-Related Defense Provisions

The United States acquired four primary defense and security rights and  responsibilities as a result the Compact of Free Association and its related  agreements: (1) the obligation to defend the FSM and the RMI against  attack; (2) the right to deny access to foreign militaries and foreign military  activity (strategic denial); (3) the right to prevent the FSM and the RMI  governments from acting in a way that is incompatible with U.S. authority  and responsibility for defense and security matters (defense veto); and  (4) the right to use certain land (i.e., Kwajalein Atoll in the RMI) for military  purposes. Pages 1 and 6 of this report state that the Compact consists of two  separate international agreements, one between the United States and  the RMI, the other between the United States and the FSM.
What GAO Found

The Compact of Free Association continues a defense arrangement that has existed between the United States and two Pacific island nations--Micronesia and the Marshall Islands--since the end of World War II. The United States has exercised only one of the four primary defense provisions contained in the Compact. That provision grants the United States the right to use part of the Kwajalein Atoll in the Marshall Islands to test nuclear missiles and space tracking operations. The United States has never been required to fulfill defense responsibilities under the other three defense provisions contained in the Compact. The Defense Department considers Kwajalein Atoll an important asset that would be costly and difficult to replicate. Ongoing negotiations over the Compact are following a course that would preserve the existing defense and security relationship between the United States and each of these nations.