The producers were lukewarm about casting Nick Nolte at first, instead preferring the more bankable Kris Kristofferson. Director Karel Reisz fought to get Nolte on board, having been impressed by seeing him in action on Reich & arm (1976).
Nick Nolte says in his biography that this movie was a box office failure, but he did not care because he was very proud of his work. And the thanked Karel Reisz for his work.
It is often believed that film's title was changed from "Dog Soldiers" so as not to be confused with the similarly titled novel of Die Hunde des Krieges (1980) by Frederick Forsyth which got made and released as a movie a couple of years later. However, the producers changed the title when they acquired the rights to use the song "Who'll Stop the Rain". The film was still released though as "Dog Soldiers" in a number of foreign territories.
The Saigon/Vietnam scenes were filmed in Mexico. A casting recruitment ad in Mexico City called for people of any Asian nationality to act in the film as Vietnamese.