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The reservist was not on active duty and not involved in coronavirus-related work for the military. His identity and other details about his death were not immediately released by officials.
He is the third member of the U.S. military to die of the virus and the first since the death in mid-April of a crew member of the USS Theodore Roosevelt aircraft carrier.
Navy Chief Petty Officer Robert Thacker Jr., 41, died of complications related to COVID-19 on April 13 at U.S. Naval Hospital Guam. More than 1,000 USS Roosevelt sailors had tested positive for COVID-19 in what had become the worst outbreak in the military.
The Roosevelt was at the center of a widening controversy that led to the firing of the ship's previous captain, the resignation of the Navy secretary, and an expanded investigation into what triggered the outbreak and how well top naval commanders handled it.
After two months sidelined in Guam, the aircraft carrier returned to sea for the first time last week and entered the Philippine Sea by May 21. Since first docking at Naval Base Guam on March 27, more than 4,000 crew members went ashore for testing and quarantine, while about 800 remained on the ship to protect and run the high-tech systems, including the nuclear reactors that run the vessel.
In recent weeks, sailors were methodically brought back on board, while the others who had remained went ashore for quarantine. At least 14 sailors have tested positive a second time, just days after getting cleared to return to the carrier.
A New Jersey Army National Guard soldier in late March was the first member of the military to die of COVID-19. In all, 6,118 members of the military have been infected with the coronavirus, of which 3,460 have recovered, according to the Pentagon.
Army Capt. Douglas Linn Hickock, 57, was a physician assistant preparing to activate as part of the pandemic response just before he was hospitalized with the virus and died one week later on March 28, according to Stars and Stripes.
The Associated Press contributed to this report.