Lifeboat

Several British and American civilians, service members and merchant mariners are stuck in a lifeboat in the North Atlantic after their ship and a U-boat sink each other in combat. Willi (Walter Slezak), a German survivor, is pulled aboard and denies being the U-boat's captain. During an animated debate, engine room crewman Kovac (John Hodiak) demands the German be thrown out to drown. However, the others object, with radioman Stanley (Hume Cronyn), wealthy industrialist Rittenhouse (Henry Hull) and columnist Connie Porter (Tallulah Bankhead), who speaks German, succeeding in arguing that he be allowed to stay. Porter, initially alone in the boat, had managed to bring her luggage with her, and her primary concern at first is a run in her stocking. She is thrilled at having filmed the battle between the two vessels, but her movie camera is the first in a series of her possessions to be lost overboard in a succession of incidents.Among the passengers is Mrs. Higley, a young British woman (Heather Angel) whose infant child is dead when they are pulled from the water after being saved by steward "Joe" Spencer (Canada Lee). After being treated by a U.S. Army nurse, Alice (Mary Anderson), she must be tied down to stop her from hurting herself. The woman, still wrapped in Porter's mink coat for warmth, sneaks off the boat while the other passengers sleep, drowning herself in the night. Willi is revealed to be the U-boat captain.The film then follows the lifeboat inhabitants as they attempt to organize their rations, set a course for Bermuda, and coexist as they try to survive. The characters start out being good-natured, cooperative, and optimistic about rescue. However, they descend into desperation, dehydration, and frustration with each other. The back stories of the characters are examined, and divisions of race, religion, sex, class, and nationality are brought to the surface. The passengers also cooperate through this stress, such as when they must amputate the leg of one of their boatmates, the German-American Gus Smith (Bendix), because of gangrene.Kovac takes charge, rationing the little food and water they have, but Willi, who has been consulting a concealed compass and reveals that he speaks English, wrests control away from him in a storm. One morning, while the others are sleeping, Smith, who had resorted to drinking seawater, catches Willi drinking water from a hidden flask. Too delirious to be taken seriously by the drowsing survivors, Gus is pushed overboard by Willi and drowns. Upon waking, the others discover Gus missing and Willi is questioned. When they notice that the German is sweating, the other passengers discover the hoarded flask in his jacket. In a spasm of anger led by Alice, they descend upon him as a group, beat him, and throw him overboard. Rittenhouse strikes him multiple times with Gus's boot to prevent him from re-boarding and, utterly disillusioned by Willi's behavior, laments, "What do you do with people like that?"The survivors are subsequently spotted by the German supply ship to which Willi had been steering them. Before a launch can pick them up, both it and the supply ship are sunk by gunfire from an Allied warship over the horizon. A frightened young German seaman is pulled aboard the lifeboat. The surviving passengers debate whether to keep him aboard or throw him off to drown as they await rescue by an approaching Allied vessel. The German sailor pulls a gun on the boat occupants but is surprised and disarmed. He asks in German, "Aren't you going to kill me?" Kovac muses, "'Aren't you going to kill me?' What do you do with people like that?"

Question: Why is it necessary for Gus Smith's leg to be amputated?
Answer: Gangrene.