Nice shooting airplane - ufo game.
What upgrades do:
-Weapons: Allows you to buy a stronger main gun.
-Shield: Adds hp to your shield, the blue thing. Your shield regenerates and takes damage before your health. Cherish it!
-Health: The green thing, the majority of your health points. Upgrading this gives you more points.
-Control: Upgrading this increases your turning speed, acceleration, and maximum speed. To avoid some enemies it is a must later in the game.
-Armor: Divides all damage of enemies by a certain number. The maximum amount of armor, for instance, divides all enemy damage by two- this is the same as doubling your health and shield. A very useful upgrade.
