The enemy doesn't start with any ships so feel free to move your Battleship forward into the reefs and use it for support fire. The Cruiser can be helpful against the enemy Battle Copters, which will come rather soon in the fight. Destroying the bottom pipes for a shortcut might be helpful, but it usually takes too long so just building Rockets from there can be a better option, and then push the north path with your combined units.
Be careful of the Rockets that will stay in the cities to the right. If you build units in the right base too soon they will get overrun by tanks unless you hide them in the forests immediately, but they will keep moving north after a couple of turns leaving you free to build anything (however it will still be in range of a Rocket).