Shooter Gallery #1: The Space Invaders Clone Show

Four fliers advertising the original Space Invaders and three of its arcade clones.

If you visited an arcade in the late '70s and early '80s, you were sure to come across a shooter or two (or ten).  So massive was the impact of Space Invaders on the video game industry that its visual style and game mechanics quickly became the reference point for an entire genre, and to some extent the video game industry in general.  This is the first in a series of entries in which I will do a retrospective on early shooters, focusing on the period from 1978 to 1980.  There is no more natural a starting place than Space Invaders.

Here I don't just mean Space Invaders the game, but rather Space Invaders the gaming phenomenon.  In what follows, I want to take off my reviewer hat for a while and look at the elements that make up the "Space Invaders" style and feel.  And what better way to do that than by looking at the games that were trying to imitate that style and feel -- the clones.

The Games

There is no hard-and-fast definition of a "clone", so there is a certain amount subjectivity in selecting games to talk about here.  In my mind, when a game is a clone, it's trying to actually be the original game, and any differences are there just to add a little spice (or avoid law suits).  More generally, it's trying to exploit a pop culture phenomenon by reproducing the affection that gamers have for another game.

This distinguishes clones from games that were just "descended from" or "influenced by" another game.  The designers of Galaxian, for example, were obviously influenced by Space Invaders, with its rows of aliens assaulting the player at the bottom of the screen.  But when you get down to actually playing it, you'll discover that the mechanics are totally different and your associations with Space Invaders are likely to take a back seat.

By contrast, if you play one of the nine games shown below, you will be thinking of Space Invaders the whole time.

Animated mosaic of gameplay clips from nine arcade clones of Space Invaders.
From left-to-right, top-to-bottom:  Space King (1978), SF-HiSplitter (1979), Rotary Fighter (1979), Attack UFO (1980), Cosmic Monsters (1979), Invinco (1979), Space Fever (1979), Space Attack (1979), Space Fighter Mark II (1980)

These are all arcade games released during the period from 1978 and 1980, at the height of the Space Invaders phenomenon.  They are rip-offs, but not just lower-tier, fly-by-night rip-offs; there are two games by Sega (Space Attack and Invinco), two by Nintendo (Space Fever and SF-HiSplitter), and even one by Konami (Space King).  Such was the popularity of Space Invaders that even the top game companies felt compelled to create copies.

The Constants

While all of the aforementioned clones added their own stylistic flourishes, some elements were always the same.  The designers clearly believed that the following things were essential to capturing the look and feel of Space Invaders.

The Basic Character Types

Every game included the player, the aliens, and the UFO.  Nothing less, nothing more.  While the player and aliens are obvious necessities, the UFO is arguably nonessential to the Space Invaders formula, seeing that it provides the player with bonus points and only appears rarely.  In modern gaming, bonus opportunities are commonplace, and you could easily imagine swapping the UFO with some other bonus feature without changing the game's fundamental mechanics.  But bear in mind that such conventions were still in their infancy in the late '70s, and the UFO may have seemed more important, both to the developers and the gaming public.


Animated demonstration of the bunker designs from some clones of Space Invaders.
Some example bunkers from the clones.  From left-to-right, top-to-bottom, Space Invaders, Space King, Invinco, Cosmic Monsters, Space Fighter Mark II, and Attack UFO.

If you're going to clone Space Invaders, you pretty much have to include the bunkers.  This is not just because it's a key visual cue, but also because removing them would fundamentally change the game mechanics.  Only one clone even changed the number of bunkers: Space Fighter Mark II, which had three instead of four.  This may have been intended to make the game more challenging, because they increased the number of aliens on the screen as well -- from 55 to 70.  

Gradual Increase in Descent Speed

High-speed clip of a game of Space Invaders with the path of one of the aliens traced out during its descent.

One of the keys to Space Invaders' success was its ability to create tension.  As the alien numbers dwindled, it gradually built to a climax by increasing the speed of the aliens (and the music). This started as an accidental feature in the original -- the microprocessor couldn't handle moving all of the aliens quickly -- but ended up being a trademark feature.  All of the clones had it as well, although the amount of speed increase varied from one game to the next.

Box-like Formations

You can imagine the clones arranging the aliens in any number of shapes and configurations, but they always went with straight-line, box-like configurations.  There was some experimentation with the arrangement of these lines.  Space Fever, for example, had a mode where the aliens descended in two separate boxes and another where the rows appeared gradually as the game progressed.  But there were no circles or triangles or anything of the sort, suggesting that the developers saw the military-like, box formations as a key visual cue.

Things That Changed: Graphics

The element that varied the most from one clone to the next was the graphics.  I don't know if this is because the clone makers thought it protected them from law suits or because it was such an easy thing to change, but they apparently believed that the exact graphical representation of the game's characters was not essential to successful exploitation of the Space Invaders phenomenon.  Let's look at them individually.


The aliens are certainly the most iconic of the Space Invaders characters, but their appearance varied a great deal in both the clones and the ports.  The animation below compiles aliens from the nine arcade clones, as well as some Space Invaders ports to home systems (MSX, NES, Atari 2600, Atari 5200, Atari 800, and ZX Spectrum).

Animated demonstration of the alien/enemy sprites from the many clones and ports of Space Invaders.
Aliens from some of the many clones and ports of Space Invaders.  From left-to-right, top-to-bottom, Space Invaders (row 1, 1 -3), Space Attack (row 1, 4-6), Space Fever (row 1, 7-9), SF-HiSplitter (row 1, 10-11 and row 2, 1-4), Space King (row 2, 5-7), Space Fighter Mark II (row 2, 8-10), Attack UFO (row 2, 11 and row 3, 1-2), Cosmic Monsters (row 3, 3-4), Invinco (row 3, 5-9), Rotary Fighter (row 3, 10-11 and row 4, 1), Atari 2600 port (row 4, 2-7), Atari 5200 port (row 4, 8-11 and row 5, 1-2), Atari 800 port (row 5, 3-8), MSX port (row 5, 9-11 and row 6, 1-2), NES port (row 6, 3-5), and ZX Spectrum port (6-11)

The original Space Invaders aliens are in the upper left corner of the mosaic, the rest of the first three rows are the clones, and then the last three rows (except for the first alien) are from the home ports.  

There are certainly common themes among the aliens; notably, a large fraction are designed to resemble sea creatures.  The arcade original had aliens that resembled a squid, a jellyfish, and a ray, so it's fitting that the ports and clones feature aliens that resemble crabs and mudskippers (SF-HiSplitter), starfish (Atari 800 port), and sea slugs (Atari 5200 port).  Not all took their inspiration from marine biology, however.  Some, like the Atari 2600 port, have an insectoid appearance.  Interestingly, the ZX Spectrum port chose to use these aliens as their prototype instead of the ones from the arcade version.

But many of these aliens look more like abstract pixel art than anything familiar.  Perhaps one of the advantages to depicting aliens in early arcade games is that there is no real prototype, and your sprites need not look realistic.  Invinco, in particular, depicts aliens that look closer to ASCII characters than anything in the animal kingdom.  

Finally, the arcade clones all chose to animate two frames for each alien, just as in the original, but the home ports were more variable.  Atari used six frames for its 5200 and 800 ports, while the ZX Spectrum port didn't animate the aliens at all.  It's odd that the clones chose to be more faithful to the original than the ports, but such is the wild, wild west of early video games.


There was also a lot of variation in the player sprite from one clone/port to another.

Animated demonstration of the player/gun sprites from the many clones and ports of Space Invaders.
The player sprites.  From top-to-bottom, Space InvadersSpace AttackSpace Fever/SF-HiSplitterSpace KingSpace Fighter Mark IIAttack UFOCosmic MonstersInvincoRotary Fighter, Atari 2600 port, Atari 5200 port, MSX port, NES port, Atari 800 port, and ZX Spectrum port.

Of course, there is only so much one can do to stylize an upward-pointing arrow, but clearly there were serious attempts to put a unique fingerprint on it.  Most of the player sprites resemble gun emplacements, with the possible exception of Space King (a tank) and Invinco (space ship?), and none of them are animated with multiple frames.


The UFO was another chance for cloners to use what little imagination they could muster to add a little spice to their rip-off.

Animated demonstration of the UFO sprites from the many clones and ports of Space Invaders.
The UFOs.  From top-to-bottom, Space InvadersSpace AttackSpace Fever/SF-HiSplitterSpace KingSpace Fighter Mark IIAttack UFOCosmic MonstersInvincoRotary Fighter, Atari 2600 port, Atari 5200 port, MSX port, NES port, Atari 800 port, and ZX Spectrum port.

Not only were the clones and ports agreed on including the UFO, but they all (more or less) agreed that it should look like a flying saucer.  Space King, which was otherwise the least creative of the clones, chose to indulge in one creative flourish by giving the UFO four spikes.

Things That Changed: Mechanics

By and large, the clones and ports didn't change the game mechanics a great deal compared to the original Space Invaders, but they did experiment a little.

Number of Aliens

I mentioned earlier that Space Fighter Mark II increased the number of aliens in formation from 55 to 70, presumably to increase the difficulty.  And they succeeded -- it is the most difficult of the clones I've looked at (by a wide margin).  Space Fever increased the number from 55 to 60, but without a noticeable increase in difficulty..

Rate of Descent

The aliens sped up as their numbers thinned in all of the games I played, but not all of them sped up at the same rate.  Attack UFO and Rotary Fighter, in particular, were not nearly as fast at the end of a stage.  This made the former game considerably easier than the original Space Invaders, while the latter partially compensated by significantly increasing the rate of fire for the last few aliens.  

Gameplay from the 1979 arcade clone of Space Invaders, Rotary Fighter.  This clip shows the player dodging bullets from the last alien.
The last alien in Rotary Fighter is a pain.

SF-HiSplitter actually had the aliens move up a few times during a stage, but still with an overall descent as the stage progressed.

Special Features

The most inventive clones were the ones by Nintendo and Sega, with SF-HiSplitter and Invinco, respectively.  They were still derivative enough that I feel comfortable calling them clones, but both featured non-trivial mechanical changes.  

Gameplay from the 1979 arcade clone of Space Invaders, called Space Fever High Splitter.
SF-HiSplitter in action.

As the name suggests, SF-HiSplitter (short for Space Fever High Splitter) confronts you with aliens that can split into two additional aliens when you hit them.  The split rate is about 50%, so you end up having to kill about 60 aliens in total.  The aliens don't descend as quickly as in the original, so the overall difficulty does not change much.

Gameplay from the 1979 arcade clone of Space Invaders, called Invinco.
Invinco in action

In Invinco, there are five rows of aliens, and only the bottom row behave like normal Space Invaders aliens.  The second row from the bottom features aliens that appear and disappear intermittently, while in the third and fourth rows, each of the aliens has a random chance of turning into a bomb when it's hit.  If you hit a bomb, it will destroy all of the aliens in its vicinity.  Finally, the top row is especially nasty, as the aliens all require three hits to kill and get smaller and smaller each time you hit them.  

Ranking the Clones

1.  Invinco (Sega, 1979)

If there is one game on this list that I would consider recommending to the general retrogaming fan, it's Invinco.  It makes enough changes to the aliens' behavior that it manages to beat down some of the monotony of the original game.  The overall experience is still highly reminiscent of Space Invaders and I wouldn't go as far as to call it an original game, but it's the only one that was decidedly better than the original.

2.  SF-HiSplitter (Nintendo, 1979)

The addition of splitting mostly just adds randomness and doesn't substantially improve the original game.  The alien splittings aren't predictable and only serve to give you more things to shoot, so the casual player isn't likely to find it much different of an experience. The game does have multiple modes, in which the aliens appear in different formations, but this also does little to improve it.

3.  Space Fighter Mark II (Data East, 1980)

The primary appeal of Space Fighter Mark II compared to the original Space Invaders is the immediately high difficulty level.  You don't have to fight through multiple waves of aliens to be challenged, and that might be appealing to skilled players. 

4.  Attack UFO (Ryoto Electric, 1980)

Attack UFO is a bit of an oddball, not because it experiments with the original formula, but because of its crude and unpolished appearance.  The bullets frequently interfere with the alien sprites (suggesting tiles, but there was no tilemap visible in MAME) and the graphics are even more simplistic than the original.  If Ryoto Electric ever produced other video games, I can't find any evidence of it on the internet, so this may have been a one-and-done situation.

Still, there is something about its flashing sprites and cartoonish sound effects that I find charming.  It's the easiest of the bunch, so this is the one I'd recommend to first-timers.

5.  Space Fever (Nintendo, 1979)

Space Fever is the predecessor to SF-HiSplitter.  It includes two additional modes that vary the alien formation a bit.  And the music is original.  But otherwise, nothing to see here.

6.  Space Attack (Sega, 1979)

Not much has changed from the original except for the visual style of the graphics and a brief bonus round between stages where the UFO moves randomly across the screen.  Not better, not worse.

7.  Cosmic Monsters (Universal, 1979)

You are being attacked by combs! As funny as that is, the game is nothing special.

8.  Space King (Konami, 1978)

Even most of the graphics are the same as in the original game.  There's really nothing new here.

9.  Rotary Fighter (Kansai Seiki Seisakusho, 1979)

Rotary Fighter creatively makes the original worse with ugly sprites.  What's more, it gives the last alien the ability to shoot continuously, creating a challenge that's more annoying than fun.

In future entries, I'll talk about how shooters evolved after the Space Invaders boom and show some successful -- and not so successful -- experiments within the genre.

[NOTE 04/29/20 -- A previous version of this article suggested that the splitting behavior in SF-HiSplitter was original, but it was probably copied from Space Invaders II, released the same year.]


  1. I'm pretty sure Nintendo just copied the splitting aliens from Space Invaders Part II.

    "The bullets frequently interfere with the alien sprites (suggesting tiles, but there was no tilemap visible in MAME)"

    Could also mean the bullet sprites lack transparent pixels. In this case, though, MameInfo seems to indicate this game uses VIC 20 hardware, which does graphics by redefining character bitmaps on the fly.

    1. Good point about the Nintendo clone, I guess the timing works out. I'll add an addendum to that effect.

      Thanks also for the note about the VlC-20 hardware.


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