The USS Tiger Shark is a U.S. Navy submarine on patrol in the Atlantic Ocean during World War II in August 1943. She receives orders to pick up survivors spotted adrift by a British PBY Catalina patrol plane. She retrieves three survivors – the British nurse Claire Paige (Olivia Williams) and two men, one of them wounded – from the British hospital ship Fort James, which had been sunk two days earlier; one of the survivors blames the sinking on a German U-boat that he briefly saw on the surface just before the Fort James suffered a torpedo hit. As they pick up the survivors, the crew of the Tiger Shark spots a German warship bearing down on them. The submarine has several encounters with the German warship and suffers damage from depth charges in the process. Later, the commanding officer of the Tiger Shark, Lieutenant Brice (Bruce Greenwood), discovers that the wounded survivor is actually a German prisoner-of-war, Bernhard Schillings (Jonathan Hartman). Brice confronts him because he thinks Schillings has been making noises to betray the Tiger Shark's position to the German warship. Brice shoots Schillings dead when the German panics and grabs a scalpel to defend himself.
Brice reveals to Paige that the Tiger Shark had sunk a German submarine tender recently and that her previous commanding officer, Lieutenant Commander Winters (Nick Hobbs), had died after the Tiger Shark surfaced to confirm the sinking. According to Brice, Winters was using a boathook to try to obtain a souvenir from the flotsam left behind by the sunken German ship when the Tiger Shark struck a submerged object, causing Winters to hit his head while reaching for his souvenir, fall overboard, and drown before he could be rescued. Brice then assumed command of the Tiger Shark.
Soon after the death of the German prisoner, those aboard the Tiger Shark begin to hear disembodied voices and experience other eerie events. While working in one of the Tiger Shark's ballast tanks, two of the submarine's officers, Lieutenant Steven Coors (Scott Foley) and Ensign Douglas Odell (Matthew Davis) have a conversation in which Odell questions the story about Winters hitting his head and falling overboard after the Tiger Shark struck a submerged object, saying that he had felt no such impact. Coors tells Odell that the real story of Winters' death is darker. Winters, on deck with only Brice, Coors, and Lieutenant Paul Loomis (Holt McCallany), had ordered them to have a gunnery party come on deck to machine-gun the survivors of the sunken German ship in the water. When Brice, Loomis, and Coors objected, a heated argument had broken out and escalated into a physical altercation during which Winters hit his head and fell overboard. In order to protect Winters' reputation, Coors asks Odell not to tell anyone. Before they leave the ballast tank, Coors dies in a mysterious accident. Soon afterwards, Loomis sees Winters' ghost aboard the Tiger Shark. He escapes from the submarine via an escape trunk while she is underwater, and dies when he is impaled on an outside railing.
A series of bizarre mechanical problems causes the crew of the Tiger Shark to lose control of the submarine, and she turns back towards the site of her sinking of the German ship, apparently of her own volition. Meanwhile, crewmen die in accidents at an alarming rate. The eerie phenomena seem related to the death of Winters, and the crew begins to suspect a supernatural influence is behind all of the Tiger Shark's mishaps and to question Brice's version of how and why Winters died.
Paige and Odell discover that the Tiger Shark mistook the Fort James for the German submarine tender and sank the Fort James instead; they also learn that Brice, Loomis, and Coors believed that they could not afford this drastic mistake to appear on their records and conspired to suppress the story, killing Winters on the deck of the Tiger Shark as he tried to save the survivors of the Fort James.
The Tiger Shark ultimately is crippled by a mounting number of accidents, and only five of those aboard remain alive: Brice, Odell, Paige, Stumbo (Jason Flemyng), and "Weird" Wally (Zach Galifianakis). Wally concludes that the Tiger Shark is haunted by a "malediction" that must be satisfied in order to escape its netherworld between heaven and hell. After the Tiger Shark arrives at the location of the sinking of the Fort James, she surfaces in a disabled condition and those aboard her detect a surface ship nearby. Brice prevents the surviving crew of the Tiger Shark from radioing the nearby ship, but Paige sneaks out on deck and tries to signal the ship with a flashlight. Brice confronts her and holds her at gunpoint. His remorse over the accident overcomes him; he admits the entire cover-up to Paige and then shoots himself in the head, falling dead into the ocean.
The ship Paige is signaling turns out to be British and picks up the four survivors of the Tiger Shark. As they look on, the Tiger Shark sinks, coming to rest on the ocean floor next to the wreck of the Fort James.Bruce Greenwood as Lieutenant Brice
Matthew Davis as Ensign Douglas Odell
Olivia Williams as Claire Paige
Holt McCallany as Lieutenant Paul Loomis
Scott Foley as Lieutenant, Junior Grade Steven Coors
Zach Galifianakis as "Weird" Wally
Jason Flemyng as Stumbo
Dexter Fletcher as Kingsley
Nick Chinlund as Chief
Andrew Howard as Hoag
Christopher Fairbank as Pappy
Nick Hobbs as Lieutenant Commander Winters
The producers of Below used the USS Silversides (SS-236), a retired World War II-era U.S. Navy Gato-class submarine that is now a museum ship in Muskegon, Michigan, for exteriors of the fictional USS Tiger Shark. The submarine was towed out into Lake Michigan for filming.
Film review aggregator Rotten Tomatoes reported an approval rating of 63%, based on 68 reviews, with a rating average of 6.2/10. The site's critical consensus reads, " Below is a creepy, claustrophobic exercise in style." The website Metacritic gave the film a weighted average score of 55 out of 100, based on 20 critics, indicating "mixed reviews". Entertainment Weekly gave the film a B+ rating, calling it a "handsome, haunting submarine thriller". Edward Guthmann from the San Francisco Chronicle gave a mainly negative review stating that the dialogue was "heavy on sarcasm and puncturing insults, never captures the World War II period but sounds ridiculously anachronistic". Variety gave the movie a mixed review stating that "the strenuous seriousness the film applies to an idea that is finally silly at its core steadily increases the impression of overwrought artificiality as matters progress".