This is not a quiet film, and it doesn't pussyfoot around.

Once the Columbia Pictures' torch lady fades from the screen, Battle: L.A. gets right to it. After all, the crowd has come to see California's biggest urban clot take it on the chin, and they've got scant patience for such time-wasters as romance, humor, sex, character development, or putting the camera on a tripod. The action -- and the noise -- are seamless wall-to-wall.

Admittedly, not many people would get their knickers in a knot over the destruction of Los Angeles. In northern California, the populace generally figures that L.A. has it coming. But this destruction isn't provincial: malevolent aliens have geared up to conquer the entire planet, and the skirmish in the Southland is only one battle in a war. However, it's the crucial conflict, as Earth's salvation (or not) eventually boils down to what happens here. It's our species against theirs, as a small squad of marines defend your inalienable rights in the ash and smoke of what was once trendy Santa Monica. Think Blackhawk Down meets War of the Worlds.

The film's plot is as straightforward as Pinocchio's proboscis. The aliens, disgusting, squishy, and strongly reminiscent of oversized sea nettles, duke it out with our military, but thoughtfully limit themselves to engagements that mostly play out with small arms fire and the occasional grenade. These aren't the Klingons, able to punch a button and dismantle a planet wholesale. The aliens' limited capabilities are what offer humanity a chance, of course.

Military matters aside, one must ask what's the motive here? Why have these gelatinous beings traveled untold light-years to flatten Lala Land?

It turns out that what they want is... the water!

The longing for liquids is an old idea in science fiction, going back more than a century to H.G. Wells, who wrote about parched Martians enviously regarding Earth's "navy crowded seas." In Wells' story, the Red Planet residents eventually got thirsty enough to launch an attack.

But Mars is relatively close. The aliens in Battle: L.A. have surely come from another star system, many thousands of times farther. Alas, schlepping across the galaxy for Earth's salty seas doesn't make much sense. That's because water is common in the cosmos. Three-fourths of the universe is hydrogen, and oxygen is incredibly abundant, too. So H2O is something you can find nearly everywhere.

In addition, water's expensive to ship, because it's heavy relative to its value. Unobtainium, the fictional mineral that motivates an interstellar mining operation in the movie Avatar, was said to be worth about $10 million a pound. You can buy drinkable water from your local utility at roughly $0.0003 per pound. Frankly, water's not particularly costly, so the shipping charges count. You're not going to haul it up out of Earth's gravity well and then rocket it hundreds of trillions of miles to your home planet when you can surely find it locally -- that's dumber than trucking landfill dirt from Mexico to Montana.

But hey, if the aliens really insist on imported water, there's plenty of it orbiting Jupiter. One of the jovian moons, Europa, is coated with twice as much liquid water as is sloshing around our planet. And Europa's not defended by gritty marines.

Besides, if these anhydrous aliens want real warehouse prices on the wet stuff, they should check out the Oort Cloud. There they'll find a trillion comets a mile across or bigger, silently swarming in the distant and undefended perimeters of the solar system -- far beyond Pluto or the Pentagon. Work it out: there's 20 thousand times as much water in the Oort Cloud as on Earth. Sure, it's frozen, but with the money the extraterrestrials save on not having to siphon our seas (not to mention the cost of munitions and veterans' benefits), they can afford to melt it when they get back home.

So someone should inform these aliens that they're making a thoroughly unnecessary visit. That might be tough, given the language barrier.

But the facts are, they're on our turf and lusting our surf. And that's the bottom line of this fast-paced action film. They're here, and they're hateful. True, I'm from northern California, and I don't mind seeing L.A. get a bit of instant urban renewal. But these aliens probably don't even have DNA. So when it's their grunts vs. our grunts, I know whose side I'm on. Oorah!