We've had a good variety of ships appear, from submarines to nuclear battlecruisers, hospital ships to fishing trawlers. Then there was that time Nathan James was tricked into thinking there was a HMS Suffolk around somewhere to help. So, what ships would you like to see in Season 3 (even if it's unlikely they'd appear.)
Personally, I'd like to see an expy of HMS Clyde come up from the Falklands via Ascension Island. It's a tiny vessel with not a lot of firepower, but with good speed and a longer range than Nathan James has. As an expy, it would have the Clyde's 30mm cannon and strengthened rear deck capable of carrying a helicopter. Having such a vessel tag along with whatever ship CNO Chandler sends to Europe to deal with the Immune Cult there, would add to the legitimacy of the operation, even if the patrol boat couldn't do much by itself.