This is for not so pro players. When you battle online, press the power button of your phone. Wait for a few seconds and then you will be disconnected but your enemy's ship will still be there. Don't worry, they won't shoot you. One more hint: battle only ships that are the same level as yours.
Fast Boat
Buy a 200 mm armour skeleton and just take off the armour (only armour). Then replace it with 600mm lightweight armour and add five angled boilers. You will now have a boat capable of reaching 160 Knots.
Fortress Pisces
Type "bsc" in codes, without the quotes.
Mikasa
At the code section enter 'Jmsdf' (without the quotes) to unlock this boat. Jmsdf stands for the Japanese Navy.