After meeting a general, war correspondent Dick Ennis (Robert Mitchum) is assigned to accompany US Army Rangers for the upcoming attempt to outflank the tough enemy defenses. The amphibious landing is unopposed, but the bumbling American general is too cautious, preferring to fortify his beachhead before advancing inland. Ennis and a Ranger drive in a jeep through the countryside, discovering there are few Germans between the beachhead and Rome, but his information is ignored. As a result, the German commander, Kesselring, has time to gather his forces and launch an effective counterattack. Ennis is with the Rangers when they are ambushed at the Battle of Cisterna. From there, the film departs from being a view of all sides and levels of the campaign to a story of a handful of survivors making their way back through enemy lines. Ennis asks what makes one human being willingly kill another. Corporal Jack Rabinoff (Peter Falk) replies that he loves it, and his lifestyle makes him live more than anyone else. Rabinoff is based on a real 1st Special Service Force soldier Jake Wallenstein, who ran an illegal brothel of Italian prostitutes in a stolen ambulance.[2] Most of the men, including Rabinoff, are killed (in reality, Wallenstein was killed by shrapnel at Port Cros during Operation Dragoon, the invasion of southern France.[3]) Ennis survives to publicly question the competence of the Allied commander.

Lee Reyes plays Hiro, Master Tetsu's (Pat Morita)'s grandnephew, who is the last of the true ninja. His granduncle sends him to apprentice under Joe Kastle, (David Bradley), who is the American Ninja, to gain experience. Hiro cares only for his Game Gear and has little interest in the ways of the ninja. Joe in addition to being the American Ninja also owns a boat. In order to meet the American Ninja, Lisa (Anne Dupont) "varnishes" his boat when in fact she was asked to "tarnish" it. While having dinner Lisa is kidnapped by Viper (James Lew) and a host of multi-colored ninjas, and so the American Ninja and Hiro sneak onto a plane to Venezuela to save her. It is revealed that Lisa is the daughter of a scientist, under the employ of Glock (Clement von Franckenstein), who is being forced to develop a nerve gas for a Latin American despot. Ninja fighting ensues. Before the American Ninja and Hiro can rescue Lisa and her father from "Viper", the mysterious ninja that appears and reappears with a puff of smoke, the American Ninja must reawaken the ancient ninja tradition within Hiro with a 5 minute training montage. Viper is defeated in a climactic airplane battle scene, and Joe returns to Los Angeles to kiss Lisa on the bow of his boat.