<P> The Treaty of the Danish West Indies was signed in August 1916, with a Danish referendum held in December 1916 to confirm the decision . The deal was finalized on January 17, 1917, when the United States and Denmark exchanged their respective treaty ratifications . The United States took possession of the islands on March 31, 1917 and the territory was renamed the Virgin Islands of the United States . Every year Transfer Day is recognized as a holiday, to commemorate the acquisition of the islands by the United States . U.S. citizenship was granted to the inhabitants of the islands in 1927 . The U.S. dollar was adopted in the territory in 1934 and from 1935 to 1939 the islands were a part of the United States customs area . </P> <P> Water Island, a small island to the south of St. Thomas, was initially administered by the U.S. federal government and did not become a part of the United States Virgin Islands territory until 1996, when 50 acres (20 ha) of land was transferred to the territorial government . The remaining 200 acres (81 ha) of the island were purchased from the United States Department of the Interior in May 2005 for $10, a transaction that marked the official change in jurisdiction . </P> <P> Hurricane Hugo struck the U.S. Virgin Islands in 1989, causing catastrophic physical and economic damage, particularly on the island of St. Croix . The territory was again struck by Hurricane Marilyn in 1995, killing eight people and causing more than $2 billion in damage . The islands were again struck by Hurricanes Bertha, Georges, Lenny, and Omar in 1996, 1998, 1999, and 2008, respectively, but damage was not as severe in those storms . In 2017, Hurricane Irma caused catastrophic damage to St. John and St. Thomas; just days later, Hurricane Maria's eyewall crossed over St. Croix . </P> <P> Until February 2012, the Hovensa plant located on St. Croix was one of the world's largest petroleum refineries and contributed about 20% of the territory's GDP . The facility stopped exporting petroleum products in 2014 . In the final year of full refinery operations, the value of exported petroleum products was $12.7 billion (2011 fiscal year). After being shut down, it has operated as no more than an oil storage facility; the closure had provoked a local economic crisis . </P>

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