Following the scattershot political satire of "Postal," "1968 Tunnel Rats" reps another departure for never-say-die multihyphenate Uwe Boll, as it's not based on a vidgame and isn't a fantasy or horror piece -- though it will be horrifying enough for claustrophobes. Instead, the straight-up actioner follows a U.S. special-combat unit trapped underground in labyrinthine, booby-trapped tunnels the Viet Cong deployed during the Vietnam War. Aptly tense and discomfiting, pic doesn't provide easy ammo for Boll haters. Still, the lack of marquee thesps and grim theme will make this well-crafted effort a challenging commercial sell.

After a short prologue showing one of the many unpleasant fates that can befall tunnel intruders, pic introduces us to the unit commanded by no-nonsense Sgt. Holllowborn (Michael Biehn). Latter is a literal take-no-prisoners type: To the disgust of some soldiers (including his second-in-command), he breaches protocol by ordering the hanging of a captured Cong sniper.

As a fresh shipment of wet-behind-the-ears newbies arrive to replace jaded veterans at this jungle camp in the Cu Chi region, pic gives quick takes on select character dynamics. But there's little room, or need, for personality detail once the pic moves into its central section.

That's a mission to infiltrate the treacherous tunnels that provide the enemy with seemingly miles to hide in and attack from. One well-hidden entrance having been found, a couple men go below -- but there's an immediate ambush. Soon, an above-ground assault forces those guarding the surface to join their colleagues below in a panicked retreat.

Training can only go so far in helping these grunts evade various traps -- from spike-lined pits to drowning pools -- plus deadly encounters with insurgents who know every inch of this ant farm for humans. Numbers on both sides rapidly dwindle, though the Americans are at a far worse advantage: The tunnels are mostly just large enough for them to crawl though --- and in one not particularly explicit but excruciating scene, a soldier trapped between two corpses must saw the limbs off one so he can wriggle past.

Though dialogue (purportedly largely improvised) is not a primary element, Boll's screenplay takes some pains to show sympathetic and fanatical types on both sides, notably in the character of a young Viet Cong mother (Jane Le) who clearly doesn't relish having to kill the enemy.

This war is hell, natch. But unlike most Vietnam flashbacks, "Tunnel Rats" sports nary a whiff of moral judgment regarding U.S. involvement in the conflict. Instead, its focus lies strictly on the visceral horror of above-ground and underground combat. Sole occasion when that approach slips into overenthusiastic horror-movie gore sees a sword sliding through a neck as if the latter were margarine-filled.

Perfs are solid, tech/design aspects excellent apart from Jessica de Rooij's somewhat pedestrian score. Standout is the widescreen lensing by Boll's usual d.p., Mathias Neumann. Verdant jungle environs of South Africa stood in for Vietnam.

Pic hardly needs the generic sensitive-female-vocal ballad over its end titles, but opening use of Zager & Evans' vintage "In the Year 2525" is perfect. Most promotional materials refer to the pic simply as "Tunnel Rats," but the onscreen title includes the (somewhat awkward) "1968" preface.

Camera (color, widescreen), Mathias Neumann; editor, Karen Porter; music, Jessica de Rooij; production designer, Sylvain Gingras; art director, Belinda Johnson; set decorator, Dylan Johnson; costume designer, Dihantus Englebrecht; sound (Dolby), Colin McFarlane; supervising sound editor, Max Wanko; visual effects, Image Engine; assistant directors, Bryan C. Knight, Taryn Collister; casting, Sunday Boling, Meg Morman. Reviewed at Another Hole in the Head, San Francisco, June 12, 2008. Running time: 96 MIN.