Considering WHAT someone is deciding whether to shoot at you, "no armor to speak of" is probably just as effective as "the heaviest possible armor they could keep afloat."
Seriously, props to the guys (and gals) who sail on those ships. It takes courage and trust in your chain of command that I can barely imagine, because I can think of few places in the armed services where your personal decisions and actions have less influence over whether you live or die. On a warship, you are stationed where it's lethal, or you aren't, you have no idea which is which until the instant it happens, and in any case you don't leave your station.
And that's just about as stark as it gets, anywhere in the service.