From StrategyWiki, the free strategy guide and walkthrough wiki

The key to strategy is staying alive. You get a new Smart Bomb and a new Ship every 10,000 points. As the game progresses, more aggressive enemies enter the playing area. To stay alive past 30,000 points, you'll need to know how to use each of the controls. The strategies below build on each other. It's essential to know strategy A before you can move to B, and so on. Once you get to strategy B, you're still using what you've learned in strategy A. You're simply adding to its depth. Remember: Your basic objective is to kill all the Landers on the screen to complete an attack wave. It's necessary to kill them quickly, so that 1) they don't mutate your Humanoids and 2) Baiters don't appear.

Contents 1 A. Beginning Strategies 2 B. Reverse Strategy 3 C. Hyperspace Strategy 4 D. Smart Bomb Strategy

[edit] A. Beginning Strategies

These are certain basic strategies that must be developed and learned as soon as possible. All of these strategies, once learned, will continue throughout your entire game.

1. Hit the Thrust and Fire buttons together. Consider these two buttons as one button. Always hit them together and hit them as fast as you can. Develop "Defender Fingers." Don't stop doing this unless you're in an instant-death situation. It's important to keep moving and to keep firing.
2. Fly low. Many top Defender players seldom fly more than two inches above the Earth's surface. It's important in adequately protecting the Humanoids.
3. Kill kidnapping Landers. Destroy the Landers when they're raising your Humanoids to the top. Don't kill your Humanoids. Once you've killed a Lander, scoop up the Humanoid and return him to the Earth for extra points. You earn 500 points for saving a Humanoid, and an extra 500 for returning the Humanoid to Earth. You also get points for killing the Lander.

[edit] B. Reverse Strategy

Reverse Strategy begins on the second screen. It should be used sparingly, and only when necessary. The most advantageous Reverse Strategy concerns the Mutants. Mutants are dangerous and difficult to kill. They also track your every move. A good way to kill them is to move up toward a Mutant, reverse and destroy it instantly. Your reversal will confuse the Mutant and stall him for an instant.

[edit] C. Hyperspace Strategy

Hyperspace becomes necessary when the score starts building, say around 30,000 points. If you've dawdled during an attack wave, several Baiters may appear. These Baiters are faster moving and faster shooting then you are. There's no need to waste a valuable Smart Bomb on them. You might as well escape them with Hyperspace. Just beware: You have no idea where you'll end up. Be prepared to move instantly as soon as you've reappeared on the screen.

[edit] D. Smart Bomb Strategy

Smart Bombs are valuable. Use them for maximum point potential. You should be able to survive without the Smart Bombs until around 30,000 points, at which point you have six of them. Wait until several Mother Ships appear on the screen at the same time. Then Smart Bomb the whole screen for 1,000 points per Mother Ship. The only other time to use the Smart Bomb is when you have no other choice. It's best to use the Smart Bomb smartly.