There are indications that severity of infection is proportional to the initial viral load. I'd imagine that being locked in close quarters on a warship would s

There are indications that severity of infection is proportional to the initial viral load. I'd imagine that being locked in close quarters on a warship would subject the sailors to a higher viral load than you'd expect in the general population, and subsequently they'd have on average more severe infections, so it could be lower than 50%.