Everyone loves a good fight, so movie history is full of classic title bouts. “King Kong vs. Godzilla,” that’s a fun one. “Batman v Superman,” that’s not. “Kramer vs. Kramer” is an Oscar-winning classic but let’s be honest, it’s a bit of a let down in the action department.

Patrick Hughes’ sci-fi thrill ride “War Machine” offers up an epic brawl between “Jack Reacher” himself, Alan Ritchson, and a giant alien robot. That’s pretty cool, and sure enough, that’s exactly what we get.“War Machine” is a shameless knockoff of John McTiernan’s “Predator,” except instead of rah-rah American heroes getting destroyed by a vaginal-faced alien, they get destroyed by a giant anime-style mecha.

The difference is “Predator” was a vicious satire of “badass” action movies, tearing down the pro-military, pro-gun genre while, ironically, doing everything those movies did, but better. Patrick Hughes picked up on the whole “doing everything those movies did” part, but seems to have overlooked the bit where “Predator” was also subversive, intelligent and full of great characters. So now we’ve got “War Machine,” a featherweight movie that tries, and fails, to stand up to a heavyweight legacy.

Still, as shameless pro-military propaganda goes, “War Machine” is a fun one. Alan Ritchson stars a heroic American soldier who, after joining the Army Ranger training program, no longer has a name. He’s just “81” now, and no, this isn’t a clever way to symbolize how military indoctrination robs people of their individual identities, “War Machine” seems to think that’s just kinda cool.

He made a pact with his brother to become Army Rangers, but 81 failed to save his brother’s life, so now he’ll stop at nothing to honor his memory by living out their dream. And by god, he’ll live it out as stoically as possible. He almost gets expelled because he’s trying too hard and doesn’t socialize. But he sticks with it and, in the final test for the Army Ranger recruits, 81 gets put in charge of a mock rescue mission to destroy a top secret aircraft.

Unfortunately, 81 was too tunnel-visioned to notice all the clunky foreshadowing about a giant asteroid cracking into pieces en route to Earth. He and his team don’t find a fake airplane, they find an honest-to-goodness UFO and, thinking it’s their target, they try to blow it up. The UFO is completely undamaged, but it sure seems pissed, so it transforms into a giant robot and starts killing all of 81’s soldiers.

Their deaths would be more dramatic if the soldiers had personalities beyond “the funny one” (Blake Richardson) or “the sensitive one” (Stephan James) or “the girl” (Alex King). But credit where credit is due, Patrick Hughes makes all the action look cool, and successfully sells how screwed these people are. Not only are they fighting an indestructible alien battle mech, but they were also on a training mission, so they only have fake ammo. It’s like Walter Hill’s “Southern Comfort,” if “Southern Comfort” took place in the “Robotech” universe.

The rest of the movie finds 81 trying to save his fellow recruits and jury-rig a way to fight back, which leads to at least one awesome car chase straight out of a “Halo” game, and a conclusion that, for a change, stops ripping off “Predator” and starts ripping off James Cameron’s “Aliens,” just for a little treat.

It’s all straightforward, b-movie fun, but Patrick Hughes comes a little too close to having a point beyond “Army Rangers good, all America’s enemies bad,” which makes it a distraction. We never find out why the aliens are attacking the Earth but we do know that they weren’t doing a damn thing to hurt us until 81’s team tried to kill them with explosives. So for a while it seems like “War Machine” will reveal that we brought this devastation upon ourselves. Sadly, no, Hughes and James Beaufort’s functional but simplistic screenplay has nothing so interesting on its mind, nor can it be bothered with anything resembling a twist.

Ritchson fights a giant robot, damn it. That’s what you clicked on and that’s all you’re gonna see. At least Ritchson is able to carry a film like this. He looks comfortable in this particular skin, playing a stalwart hero whose still waters run (vaguely) deep. When “War Machine” finally weeds out the chaff and pits him against the robot, mono-a-mecho, we buy it. We’d have preferred to buy something smarter, but this is a decent substitute, especially since it’s on Netflix and we’re not paying full price.

“War Machine” is, in all fairness, what it says on the box. This is a machine that promotes war. It says our American soldiers are all awesome, our enemies are all evil, and what’s more, they don’t deserve our empathy. Hey, maybe you should think about enlisting too, so you can also kill them. Wouldn’t that be a cool thing to do?

Needless to say the release date is unfortunate for something like this, what with the whole “America starting a war” thing. As such, “War Machine” may be hard to stomach as the big, silly, brainless sci-fi action movie it obviously wants to be. But if you can accept the fact that it’s big, silly and brainless, and nowhere near as good as its obvious influences, and also that it’s shameless propaganda, it’s still possible to have a good time.