It came a week after another US Navy sailor stationed in southern Italy contracted COVID-19, which has killed more than 3,700 people worldwide including nearly 70 in the United States.
"A Sailor assigned to the amphibious assault ship USS Boxer (LHD 4) tested 'presumptive positive' for Coronavirus Disease 2019 (COVID-19), marking the first case for a sailor aboard a Navy ship," the Navy said in a statement on Sunday evening.
The sailor was in quarantine at home, it said, adding that "personnel that the individual immediately identified having close contact with have been notified and are in self-isolation at their residences."
The Navy said that the US Centers for Disease Control and Prevention would need to confirm the positive result.
The USS Boxer is currently in port at a naval base in San Diego, according to local media.