@Tbar
Right, you have to do daily logins and then you’ll get the “submarine token” that will unlock the 3 subs with commanders. It’s RNG I believe, so you might get it on the first shot – or like me – took me 7 days to unlock the subs.
Once you unlock the subs, there is a special battle type for subs where you then get to pick 1 of 3 subs you unlocked.