Just A Damned Soldier.

After their mission is overrun by North Vietnamese forces, a missionary couple, their Australian guide, a South Vietnamese major, a brothel owner and her daughter all get in the mission's battered school bus and try to make their way to safety. Soon after leaving, however, their bus is commandeered by three US Marines trying to get back to their base at De Nang. To reach their destination, they must fight through most of the North Vietnamese army.