Anchors are required to advance in the tech tree. Each level has a total of seven anchors that can be collected. To get additional anchors, replay levels under the other difficulty settings.
Flying ace
Keep repositioning the "Flying Ace" hero during a level to get the most benefit from it.
Tech tree
You can tailor the tech tree before or after a level to be better suited for your next opponent. Reset the tech tree, then select upgrades for towers that are stronger against what you are facing.
Towers
When a level first begins, you are allowed to sell and reposition towers without any money loss. Then, tap "Start" to begin game play.
Upgrades
The "Double Trouble" upgrade for the turtle cannon is very powerful. The "Sea Fog" power is useful to slow down the action and get some extra hits on your opponent.
