The enemy realized that on the ground and in the air they have no chance. And they began to attack in the water. Build defenses and beat back the crowds of enemies. For the destruction of each of the ships, you'll receive the money. The better the tower, the more it will cost. Sometimes it is more profitable to improve the building than to buy new ones. In order not to wait for a moment before each wave, you can start it prematurely, or some waves at the same time.