Military SF in its literary form is unmistakably militaristic. Chains of command and snappy uniforms, decisive battles and epic campaigns, ensigns swabbing the deck and generals inspecting the troops... all extrapolated to their 30th-century (or whenever) equivalents. There’s a reason why Honor Harrington is called a futuristic Horatio Hornblower: her world is not so different from his, and he could probably fill an officer’s slot on her ship without too long an orientation period.

There’s no movie equivalent of those books, though, not as a genre. Ask the average SF fan to name some “military SF” flicks, and chances are two films will be named quickly: 1986’s Aliens and 1997’s Starship Troopers. Aliens, of course, is James Cameron’s brilliant depiction of an outfit of Colonial Marines in a “bug hunt” for acid-bleeding aliens. I’ve never been a Marine, of course, but the film has the ring of truth to it from the soldiers and their attitudes, to their distrust of the inexperienced new lieutenant who barges into their team; even one of the film’s more speculative elements—female Marines fighting alongside the men—succeeds fabulously: there’s more than just one token girl, and they’re as believably tough as the guys. That aspect surely influenced Paul Verhoeven a decade later, when he departed from Heinlein to introduce female soldiers in his Mobile Infantry in Starship Troopers, a satire on a fascist future Earth society dominated by its military forces. (That’s an ironic bit of turnaround: Heinlein’s novel surely influenced aspects of Aliens; Cameron may have borrowed the term “bug hunt,” for one, from the 1959 book.)

Think on “military SF” a bit more, and you might concede that the Star Trek films qualify, perhaps as a mirror image to Starship Troopers’ extrapolation: the military in the 23rd and 24th century here has morphed into a kinder, gentler, paramilitary science and exploration corps that can blow stuff up if necessary but is not primarily a fighting force—Starfleet doesn’t seem to have infantry or cavalry or Marines or any kind of grunts to put on the ground if needed (good thing it never seems to be needed).

Dig a bit deeper, into military films that, on second glance, could be considered SFnal, or into SF films that, on second glance, could be considered military, and we end up with two basic scenarios: contemporary 20th- or 21st-century military forces face SFnal situations; and stories set in the future that feature characters who serve or have served in their equivalent of a military force, though the stories in which they appear are not overly concerned with military procedures or hierarchies.

The second scenario is by far the more infrequent one. Han Solo is a former Imperial trooper—though that tidbit isn’t revealed in the films; you have to turn to the Brian Daley novels about the character to learn that—but remnants of his uniform seem to be the only lasting remnant of that experience. And while 1977’s Star Wars is about a galactic war, it isn’t military SF—its hero is an interloper into the military arena of the Rebel Alliance, in fact; one can imagine some up-and-coming young pilot who’s paid his dues in the Alliance ranks, steaming over the fact that he didn’t get to move up to fight in the Death Star battle because Luke Skywalker got the X-wing fighter that should have gone to him.

And then there’s Mal Reynolds (played by Nathan Fillion), in the recent Serenity. A former army platoon sergeant, his experience on the losing side of the war he fought colors absolutely everything about his character. But the war is over, and though we see hints of the militaristic structure of the ruling Alliance, that’s not what the film is even remotely about.

The first plot, on the other hand, has been a standard of popcorn SF and SF-horror films since the U.S. Army battled giant radioactive ants in 1954’s Them!—whether it’s alien invasion or mutant-monster attack, men in uniform with guns who haven’t even considered, never mind trained for, such contingencies are called out. Recent films that fall into this subgenre tend to feature somewhat more savvy professional fighters, guys who grew up watching exactly the kind of cheesy SF flicks they now find themselves in: Will Smith’s fighter pilot in 1996’s Independence Day is a lot less rattled by the idea of aliens and seems to treat flying against them almost as a video game.

Sometimes the speculation contemporary military films engage in is so close to our own reality that you can’t even be sure what’s conjecture and what’s real. Does the technology actually exist that makes the experimental Russian sub Red October run so quietly? And does it make 1990’s The Hunt for Red October any more or less SFnal if it does? After all, the plot hinges on new and innovative uses of technology, from the Red October’s noise-smothering baffles to the clever way Courtney Vance’s naval sonar operator learns how to find the sub despite its stealth. Can we consider 1998’s The Siege military SF? In the wake of terrorist attack in New York City, an army general played by Bruce Willis polices martial law in Brooklyn and rounds up Arab-Americans—if the film’s speculation is entirely in the realm of how the military exists within the society at large, is that enough? How about 2000’s Space Cowboys, which pits out-to-pasture Air Force pilots against younger Air Force hotshots in a story about secret satellites and a surprise trip to the moon? Has the real world become so SFnal that it’s getting hard to find the boundaries where SF begins?

Some contemporary military SF leaves no doubt as to its provenance, however. The Final Countdown, from 1980, throws a modern aircraft carrier (at least, modern for 1980) back into World War II; with all its ethical wrangling and scientific debate over the integrity of timelines, this is one of the more thoughtful military SF films of recent decades, and one of the few that more resembles literary SF than action movies. 1994’s Stargate throws Air Force special forces through a wormhole to a distant planet, where they fight an alien: definitely SF. Terminator 3: Rise of the Machines, from 2003, gives us a close look at the military machinations that produced SkyNet and the first generation of the smart machines that would later attempt to wipe out humanity: definitely SF. That same year, X-Men 2: X-Men United showed us a hint of the secret military project that created Wolverine: definitely SF.

Why don’t we see movie versions of Honor Harrington or Miles Vorkosigan, or original creations in a similar vein? Their stories are too episodic, perhaps, more suited to television than feature films, though of course we haven’t seen them on television, either. Or Hollywood may simply find the cross-genre character of military SF too difficult to sell to mainstream audiences. I don’t doubt, though, that many movie lovers, whether they consider themselves SF fans or not, would love to see more films like Aliens—more good films like Aliens, that is: the nonstop slew of poor imitations, like the recent Doom, suggests that Hollywood at least recognizes the potential of the genre. With a few fresh ideas in the mix, it might eventually succeed in creating it.