On: U.S. Navy test shows 60 percent of carrier crew have coronavirus antibodies

[vnchr]

Herd immunity halts transmission after a point. The flu is between 33% and 44%. Covid-19 has some wide estimates for the threshold, between 29% and 74% according to the two studies referenced here: https://en.wikipedia.org/wiki/Herd_immunity#Mechanics

[s1artibartfast → vnchr]

Herd immunity and r0 would be significantly different on a ship