It doesn't say how long they've been at sea, but I'm thinking they had to make a port call somewhere to get infected.
U.S. warship heads to port after coronavirus outbreak
At least 18 sailors aboard a U.S. Navy destroyer have tested positive for the new coronavirus, U.S. officials said on Friday, dealing another blow to the military as it faces fallout over its handling of an outbreak on an aircraft carrier last month.
www.reuters.com