Damge, who will win?

Probs the destroyer.

I know thr destroyers in this game are usually used as either scout ships or as anti-sub escorts for larger ships. Subs are just good at sinking unescorted battleships and convoys, plus as recon units for scouting landing sites.

The destroyer has great anti-sub values. The sub has decent anti-ship but it isn't high enough in this case.

I can not say which will win in that scenario. I have heard that the first unit, between subs and destroyers, that fires will do more damage and that gives them an edge in the final outcome.