Continuing through my favorites, I am reasonably certain that this was a game developed only for home computers, and probably only in Europe. That was supposed to be the plan from the start with this Atari ST feature: to focus on those games that were exclusive to, if not the Atari ST (they and the Amiga shared everything, pretty much), then for UK home computers in general. I'm usually fighting between wanting to cover something people have heard of, engendering some discussion in the comments as people convey their own history with and opinions on the game in question, or introducing something most of you haven't seen before in an elucidating and hopefully not-too-hipstery fashion. Then again, I'm not sure "I was into this before it was cool" is going to necessarily fly with a Warhammer 40k game.
But I'm getting ahead of myself.
Space Crusade
The original Space Crusade was actually a board game: Games Workshop put it together as a sister product for HeroQuest, and is meant to be a gateway to the considerably more in-depth world of Warhammer 40k. This game doesn't quite have as many rules as its famous wargaming older brother, but introduces franchise concepts like SPOICE MAREENS, orks, heavy hit dice, the Imperium of Man, and the enigmatic and destructive force of Chaos.
In a nutshell, it allows up to three players (and an additional player would be in control of the enemy units, like a DM) to each take one of three Space Marine chapters - the Blood Angels (red), the Imperial Fist (yellow) and the Ultra Marines (blue) - and complete missions for the Imperium. There wasn't any big connecting tissue, and each of the missions took place on a different "space hulk", which simply amounted to different configurations of the same board.
The 1992 computer game adaptation by Gremlin Graphics is remarkably faithful, allowing up to three players to pass-and-play at home, either cooperating with or competing against each other for the primary and secondary mission objectives as well as the highest kill count and other score boosting requirements. If your squad scores highest, your commander gets a promotion. Score too low and he'll kill himself in shame. As to the core rules of the game, we'll get into that as soon as the screenshots start coming. Like now. (As always, check out its spooky (and bloopy) theme.)
Without exaggeration, Space Crusade is my favorite game for the Atari ST and the chief reason I still enjoy squad-based SRPGs to this day, especially ones where I only have to worry about the protagonist dying. It's perfectly balanced: while you can get to grips with the rules within a few minutes, as its 40k rules were deliberately simplified to proper befit a board game, it's still as challenging as hell and prone to all sorts of mishaps. Yet, even if you were to crash and burn towards the end like I did, a single mission usually takes at most thirty minutes to an hour. While its limitations are unlikely to hook hardcore TBS fans for too long, it was a perfect primer for a younger me, and probably still to anyone who is put off by Fire Emblem or Final Fantasy Tactics's complexity.
While not the most gregarious child, I did also appreciate Space Crusade's multiplayer options, though things could get awfully heated if it looked like one of the space marine chapters was going to go home empty-handed. If push came to shove, you could always start gunning down each other marines like some turn-based strategy Bomberman.
Were I any more suggestible, I'd probably have a huge collection of 40k miniatures because of this game too. Glad I dodged a plasma ray there.