The building blown up in the opening sequence in the film, was an old San Francisco Fire Department building that was scheduled for demolition. Sam Peckinpah filmed the implosion from the upper floor windows of the Hyatt Regency Hotel, which was directly across the street.
Sam Peckinpah was assigned to direct this film by Mike Medavoy, the head of United Artists at the time. Medavoy believed in Peckinpah's abilities, but knew that it was virtually impossible for Peckinpah to get a job with any of the studios, as he had alienated virtually everyone in Hollywood by that time. When this project came along, Medavoy knew it was perfect for Peckinpah, and gave it to him, but under the conditions that he worked under Medavoy's strict supervision. Peckinpah agreed.
In preparation for the film, Robert Duvall and James Caan took lessons in mastering their characters' skills with Duvall taking lessons in using a rifle with infrared scope, and Caan learning to disarm the film's villains with the use of a cane.
Most of the film's action sequences were filmed in San Francisco's Chinatown on Waverly Street, the site of what became known as the "Tong Wars", vicious battles between rival groups of Chinese, that took place in Chinatown shortly after World War I.
Martial Arts expert Hank Hamilton developed a new method of instructing the actors specifically for this film, in order to technically direct the savage kung fu battle on the decks, and also from the crow's nest of the Mothball fleet.
During the escape from Chinatown in the modified cab, one of the passengers mocks the driver by saying, "Who do you think you are? Stiriling Moss?" Moss was a British Formula One racing champion who retired in 1961. At the time of original release, it would have been a more universally recognized comparison, not the obscure footnote it has become in the new millennium.
James Caan and Robert Duvall appeared in numerous television and movie productions, most notably Countdown (1967), The Rain People (1969), The Godfather (1972), The Godfather: Part II (1974), and this movie.