It's based on a novel for juveniles by Robert A. Heinlein. I read it to the point of memorization when I was in grade school. I have improved since then, but the story has not. Early in the next millennium, mankind is engaged in a war for survival with the Bugs, a vicious race of giant insects that colonize the galaxy by hurling their spores into space. They exist not as an alien civilization but as pop-up enemies in a space war.
Human society recruits starship troopers to fight the Bug.
Their method is to machine-gun them to death. This does not work very well. Three or four troopers will fire thousands of rounds into a Bug, which like the Energizer Bunny just keeps on comin'. Grenades work better, but I guess the troopers haven't twigged to that. You'd think a human race capable of interstellar travel might have developed an effective insecticide, but no.