Why Space Invaders Speeds Up as the Aliens Disappear

You start a wave of Space Invaders facing 55 aliens in five rows of eleven, shuffling sideways at a slow, almost polite pace. Clear 50 of them and the last few start racing across the screen, and the final invader moves so fast that most players miss it three or four times. Why Space Invaders speeds up as the aliens disappear is one of the best stories in arcade history, because the most famous difficulty curve of 1978 was never designed as one.

I have spent more hours than I would like to admit on original cabinets and faithful emulations, and the more you understand what the machine is doing, the better you play. Here is what is actually happening on screen, and how to use it.

The Hardware Behind Why Space Invaders Speeds Up

Space Invaders, designed by Tomohiro Nishikado and released by Taito in 1978, ran on an Intel 8080 processor. That chip was modest even then. Drawing and moving 55 sprites, plus your cannon, the shields and every missile, stretched it to its limit.

The game handles this by moving one invader per screen refresh. With all 55 alive, it takes 55 updates before the whole formation has stepped once. When only 10 remain, the formation steps in 10 updates. With one invader left, that invader moves on every single update. Nothing in the code says "go faster". The work simply gets smaller, so each alien gets its turn more often.

Nishikado has said he noticed the acceleration during development and kept it, because it made the end of each wave tense. That decision shaped how arcade games handled difficulty for years.

How the March and the Heartbeat Sound Work Together

The famous four note bass loop is tied to the formation's movement. Each step plays the next note. As the formation speeds up, so does the music, which is why the end of a wave feels like your pulse is rising with it.

This is useful information, not just trivia. The sound tells you how fast the aliens are moving without looking away from your cannon. Experienced players often keep the volume up for exactly this reason.

Points Per Row and the Mystery Ship

Not every target is worth the same. Here is the standard scoring:

A full wave of 55 invaders is worth 990 points. A single well timed mystery ship can add almost a third of that. The ship's value is tied to how many shots you have fired, not to luck. The widely documented pattern is that the 23rd shot of a wave, and then every 15th shot after it, scores the full 300 if it hits the ship. Counting shots sounds tedious, but top players do it as naturally as breathing.

Why Clearing the Bottom Row First Is Usually Wrong

New players tend to shoot whatever is closest, which means the bottom row. It feels safe, because those aliens are nearest to you. It is also the slowest way to play.

The formation only drops a line when its outer edge hits the side of the screen. If you clear the outside columns instead, the block becomes narrower and has to travel farther before it touches the wall. That buys you more time before every drop. Most strong players carve away the left and right columns first, then work inward.

The bottom row still matters later, because it decides how low the formation can get before an invader lands. But clearing columns early gives you a wave that stays high for longer, which is exactly what you want when the speedup arrives.

Handling the Last Few Invaders

The final invader is where most lives are lost. A few habits help:

1. Leave a slow one for last. Try to finish with an alien near the top of the screen, so it has farther to fall.
2. Lead your shot. At full speed, aim one to two alien widths ahead of where it is heading.
3. Do not chase it. Park your cannon and wait for it to come back across. Running under it usually means missing behind.
4. Watch the wall. When it touches the edge, it drops and reverses. That moment is the easiest shot you will get.

Shields Are a Resource, Not a Fortress

The four bunkers erode from both sides: your own missiles chip them from below, and alien bombs eat them from above. Many players hide behind a shield for the whole wave and wonder why it is gone by the third.

A better approach is to shoot through a small gap you make in one shield on purpose. That hole lets your missiles pass while the rest of the bunker still blocks bombs. Once the formation drops low enough to touch the shields, the invaders destroy them anyway, so use them early while they still have value.

One more detail worth knowing: alien bombs come in three shapes, and they do not all behave alike. The plunger shaped shot tends to track toward your column, while the other two fall from set columns. When you see a plunger leave the formation, move sideways rather than ducking behind a damaged shield. That single habit saved me more lives than any shield trick.

Where to Play the Original Today

Original upright cabinets still turn up in retro arcades and barcades, usually for a quarter or two per game. Official compilation releases from Taito have also brought the 1978 version to modern consoles, often with a filter that mimics the coloured cellophane strips the first cabinets used over a black and white monitor. If you enjoy reading how old machines think, our breakdown of how the Pac-Man ghosts decide where to chase you is a natural next read.

Frequently Asked Questions

Was the speedup in Space Invaders a bug?

Not exactly. It is a side effect of the hardware moving one invader per update. The designer noticed it and chose to keep it, so it is better described as a happy accident that became a feature.

Does the mystery ship really depend on shot count?

Yes. Its point value follows the number of shots fired in the wave. The 23rd shot, and every 15th one after that, scores 300 if it hits the ship, which is why high level players count every press.

Why does the game get harder on later waves?

Each new wave starts the formation lower on the screen, so the aliens have less distance to cover before reaching you. The speed rules stay the same, but you get less time to use them.

The Practical Takeaway

Clear the outside columns first, count your shots for the 300 point ship, keep the sound up, and wait for the last invader instead of chasing it. Once you see the speedup as a predictable rule rather than chaos, the end of every wave gets calmer. For more classics that still reward careful play, browse our retro and arcade guides.