Four American Seabees land on a Pacific island held by a small, bored, left behind Japanese garrison. Their mission is to determine whether an airfield can be built on the island, and then get out and report back. However they run into the Japanese almost immediately and wind up running and fighting for the rest of the film.
The movie fails on many levels.
It is not credible as an action movie. The Americans hide almost effortlessly from the Japanese, who seem listless and lackluster in their pursuit. The Americans' Tommy guns never seem to need reloading. They talk in almost normal voices in spite of nearby Japanese. They almost always spot the Japanese first and hide successfully in places where they should be spotted pretty quickly.
It's just as bad as a character movie. The officer in charge is irascible and arbitrary. The men aren't entirely believable. The Japanese, even though they have small parts, are better presented as people. The single girl in the story, who is completely unbelievable as a native islander, is given a totally predictable and mechanical part.
The plot lurches from action to action, almost as if the writers wrote a scene, the company played it, and then the writers asked themselves, Now what should we do next?
Perhaps, as others have suggested, this was a pilot for a TV series that was never made. It has a few good touches, but they are overwhelmed by the failures.