Galaga

You're under attack! The Galagans are reclaiming planets they lost during a centuries-old interstellar war - and now they want yours! And you're ready to fight to the bitter end to protect it!

So you join the Intergalactic Warrior Fleet. Without training, you're assigned to your first combat mission - and on-the-job is the only way to learn. Shaking in your boots, you accept the assignment and board your Intergalactic Command Ship.