There’s lots of action in “Basic,” and the movie wouldn’t be so bad if it were honest enough to acknowledge that’s its only reason for existing. But “Basic” struggles mightily to earn those fancy adjectives “complex” and “multilayered,” and it’s neither. During a routine exercise in the jungles of Panama, a group of elite Army Ranger trainees, led by tough-as-old-boots commanding officer Samuel L. Jackson, suddenly seem to go bonkers, shooting at one another and blowing up their surroundings with grenades.

Brian Van Holt and Giovanni Ribisi are the only survivors, and they both spend the first section of the movie refusing to talk at all, only to tell conflicting stories when they finally do spill the beans. Apparently, they too have seen many, many movies in which “Things are not always as they appear,” and so John Travolta, a former Ranger who is now a possibly corrupt DEA agent, is brought in to worm the truth out of them.

Connie Nielsen, an actress who has lent class and gravity to just about every movie she’s appeared in (from “Mission to Mars” to “Gladiator” to the unreleased French film “demonlover”), plays the Army captain assigned to “officially” investigate the case, and she has a tough time accepting the renegade Travolta. But not even she can improve “Basic.”

The script, by James Vanderbilt, piles one implausibility atop another under the auspices of building suspense. One survivor claims a beleaguered soldier who had been taunted by Jackson killed the sergeant and then tried to bully the others into helping him cover up his mistake; the bodies were subsequently blown away by a hurricane. The other soldier has a significantly different story, which means we get to see two versions of the bloody jungle skirmish (told in flashback sequences) — twice as nice if you like that sort of thing.