In the future, all plant life on Earth has become extinct. A few specimens have been preserved in enormous, greenhouse-like geodesic domes attached to a fleet of American Airlines space freighters, currently just outside the orbit of Saturn. Freeman Lowell (Bruce Dern), one of four crewmen aboard the Valley Forge, is the resident botanist and ecologist who carefully preserves a variety of plants for their eventual return to Earth and the reforestation of the planet. Lowell spends most of his time in the domes, both cultivating the crops and attending to the animal life.
Orders come from Earth to jettison and destroy the domes (with nuclear charges) and return the freighters to commercial service. After four of the six domes are jettisoned and blown up Lowell rebels and opts instead to save the plants and animals on his ship. Lowell kills one of his crew-mates who arrives to plant explosives in his favorite dome, with his right knee seriously injured in the process. He traps the remaining two crewmen in the other dome, just as it is jettisoned and destroyed.
Enlisting the aid of the ship's three service robots, called drones, Lowell stages a fake premature explosion as a ruse and sends the Valley Forge careening towards Saturn in an attempt to hijack the ship and flee with the last forest dome. He then reprograms the drones to perform surgery on his leg and sets the Valley Forge on a risky course through Saturn's rings. Later, as the ship endures the rough passage, Drone 3 (later nicknamed Louie) is lost, but the ship and its remaining dome emerge relatively undamaged on the other side of the rings.
Lowell and the surviving drones – which he nicknames Huey (Drone 2) and Dewey (Drone 1) after the cartoon characters – set out into deep space to maintain the forest. Lowell also reprograms Huey and Dewey to plant trees and play poker. Huey is damaged when Lowell accidentally collides with him while driving a buggy recklessly, and Dewey sentimentally refuses to leave Huey's side during the repairs. As time passes, Lowell is horrified when he discovers that his bio-dome is dying, but is unable to come up with a solution to the problem. When the Berkshire – another space freighter waiting to see if the Valley Forge has survived the trip – eventually re-establishes contact, he knows that his crimes will soon be discovered. It is then that he realizes a lack of light has restricted plant growth, and he races to install lamps to correct this situation. In an effort to save the last forest before the Berkshire arrives, Lowell jettisons the dome to safety. He then detonates nuclear charges, destroying the Valley Forge, the damaged Huey and himself in the process. The final scene is of the now well-lit forest greenhouse drifting into deep space, with Dewey tenderly caring for it, holding a battered old watering can.Bruce Dern as Freeman Lowell
Cliff Potts as John Keenan
Ron Rifkin as Marty Barker
Jesse Vint as Andy Wolf
Mark Persons as Drone 1 (Dewey)
Cheryl Sparks and Steven Brown as Drone 2 (Huey)
Larry Whisenhunt as Drone 3 (Louie)
Trumbull had been involved with creating effects for 2001: A Space Odyssey. Director Stanley Kubrick had wanted the Stargate sequence of that film to be about Saturn, but there were technical difficulties in getting the special effects for it finished in the limited time available. The Saturn idea was scrapped, and Kubrick substituted Jupiter instead. Trumbull developed the sequence after production, and it was recreated for Saturn in Silent Running.
The interiors were filmed aboard the decommissioned Korean War aircraft carrier USS Valley Forge (LPH-8), which was docked at the Long Beach Naval Shipyard in Long Beach, California. Shortly after filming was completed, the carrier was scrapped. The forest environments were originally intended to be filmed in the Mitchell Park Domes in Milwaukee, Wisconsin, but the production budget forced the sequences to be shot in a newly completed aircraft hangar in Van Nuys, California. Trumbull stated in the commentary accompanying the DVD release that the geodesic domes containing the last forests of Earth's future on the Valley Forge were based on the Missouri Botanical Garden Climatron dome.
Three freighters are shown in the film, the Valley Forge, the Berkshire, and the Sequoia. Five other ships that carried domes – the Yellowstone, Acadia, Blue Ridge, Glacier and Mojave — are also mentioned. Each ship features a designation on the hull which notes the area from which some of the flora and fauna samples were taken. The Valley Forge is listed as "Bahia Honda Subtropical", indicating at least some specimens were taken from this area of the Florida Keys.
The model of the Valley Forge was 25 feet (7.6 m) long, and took six months to build from a combination of custom castings and the contents of approximately 800 prefabricated model aircraft or tank kits. After filming was completed, American Airlines expressed an interest in sending the model on the tour circuit, but this was not feasible due to the fragile nature of the model (in fact, during filming pieces of the model kept falling off). The ship was subsequently disassembled after several years sitting in Douglas Trumbull's personal storage facility. Several pieces, including the domes, wound up in the hands of collectors. Several domes survive, including one that now rests in the Science Fiction Museum and Hall of Fame in Seattle, Washington, and another which was sold at auction in 2008.
The three drones were played by four bilateral amputees, an idea inspired by Johnny Eck, a sideshow performer of the early 20th century who had been born without lower limbs. The 20-pound (9.1 kg) drone suits were custom-tailored for the different actors. The suits are in Douglas Trumbull's personal collection.
The sound effects, including the drones, were created by uncredited composer Joseph Byrd. They were generated on a modified ARP 2600 synthesizer with added Oberheim Expander Modules.
The soundtrack was written by bassoonist and P. D. Q. Bach creator Peter Schickele. It contains two songs written by Schickele and Diane Lampert — "Silent Running" and "Rejoice in the Sun" — which were performed by popular folk singer-songwriter Joan Baez. The two songs were issued as a single on Decca (32890). In addition, an LP was released on Decca in 1972 (DL 7-9188) and later reissued by Varese Sarabande on black (STV-81072) and green (VC-81072) vinyl. In 1998, a limited-release CD by the "Valley Forge Record Groupe" included an additional track with the spoken introduction "God Bless These Gardens". A CD with audio restoration was released in 2016 by Intrada, Special Collection Volume 369.
The film has a generally positive rating on Rotten Tomatoes, with 67% of 27 critics giving good reviews. Praise is mainly focused on the special effects and Bruce Dern's performance, while the script and storyline are criticised as weak. In his New York Times review, Vincent Canby says this "is no jerry-built science fiction film, but it's a little too simple-minded to be consistently entertaining". UK film critic Mark Kermode has frequently named the film as one of his personal favourites in his BBC blog, on more than one occasion stating his preference for it over 2001: A Space Odyssey.
In 2008, the American Film Institute nominated this film for its Top 10 Science Fiction Films list.
A novelization of the film was published by Scholastic Books in 1972. It was written by Harlan Thompson, a long-time children's book author, based on the screen story and screenplay by Cimino, Washburn, and Bochco.