1941

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On Saturday, December 13, 1941 at 7:01Â a.m., a woman goes swimming somewhere on the California coast, only to find a Japanese submarine surfacing beneath her. The submarine crew believes they have arrived in Hollywood, and the vessel submerges while the woman swims to safety.
Later that morning, a 10th Armored Division M3 Lee tank crew, consisting of Sergeant Frank Tree, Corporal Chuck Sitarski, and Privates Foley, Reese, and Henshaw, are at a restaurant where dishwasher Wally Stephens works. Wally is planning to enter a dance contest with Betty Douglas, against the wishes of Ward, her father. Sitarski takes an instant dislike to Wally, particularly his civilian attire, and trips him. A fight ensues, leading to Wally losing his job. Wally later takes his friend Dennis shopping for a zoot suit and steals one.
In Death Valley, cigar-chomping, unruly Army Air Forces Captain Wild Bill Kelso lands his Curtiss P-40 fighter near a grocery store and gas station; while refueling, Kelso accidentally blows up the station.
In Los Angeles, Major General Joseph W. Stilwell attempts to keep the public calm. At a press conference at Daugherty Field in Long Beach, Captain Loomis Birkhead is attracted to the General's secretary, Donna Stratten. He lures her into a bomber to seduce her, aware that Donna is sexually aroused by airplanes. When his attempts at seduction fail, she punches him and accidentally knocks him out; as he falls, he lands on a bomb release control, sending a bomb rolling towards the podium just as the General promises, "There will be no bombs dropped here." It explodes, though Stilwell escapes.
At the Douglas family home in Santa Monica, Wally is told by Betty and her friend Maxine, both USO hostesses, that he cannot enter the USO dance because he is not a serviceman. Wally is forced to hide when Ward shows up. Sgt. Tree and his tank crew arrive to deliver an anti-aircraft battery; Sitarski is attracted to Betty and about to ask her to the dance when Wally falls on him from a loft. Ward and Sitarski dump him in a garbage truck.
The Japanese sub becomes lost trying to find Los Angeles when the ship's compass is broken. A landing party looking for "Hollywood" instead captures Hollis "Holly" Wood, who reveals only his name, occupation, and social security number. They see he has a small Cracker Jack compass, but he swallows it. Hollis escapes, hoping to find the authorities.
That night, Stilwell goes to a showing of Dumbo. Birkhead and Donna are at the 501st Bomb Disbursement Unit in Barstow, where Colonel "Mad Man" Maddox shows them the unit's aircraft. Maddox, convinced the Japanese are sending paratroops into the hills near Pomona, lets Birkhead and Donna borrow a plane, assuming they are going on a reconnaissance flight. Donna, stimulated by the entire experience, eagerly ravishes Birkhead during the flight.
Outside the USO, Sitarski kicks aside Wally and drags Betty into the dance. Maxine tags along. Wally sneaks in by wearing a stolen Shore Patrol uniform, He steals away Betty and they win the dance contest whilst evading Sitarski, who is pursued by Maxine. As the contest ends, Sitarski finally punches Wally, setting off a brawl between soldiers and sailors.
Sgt. Tree arrives with his team, just as L.A. goes to Red Alert with an unknown aircraft in the air. At the Douglas' home, Ward spots the sub. Birkhead and Donna fly over L.A., causing anti-aircraft batteries to open fire. Kelso shoots down Birkhead's plane, which lands in the La Brea Tar Pits (the crash only momentarily interrupting his tryst with Donna). Kelso then sees the submarine, only to be shot down by two spotters (who were positioned on the Ferris wheel) who mistake his plane for a Japanese fighter.
Sitarski is about to make off with Betty when she is rescued by Wally, who knocks Sitarski cold. They find Kelso, who informs them about the sub. Wearing an army uniform, Wally commandeers Tree's tank and heads toward Pacific Ocean Amusement Park. Ward begins firing at the submarine, causing massive damage to his house in the process. The submarine returns fire, hitting the Ferris wheel, which rolls into the ocean. The tank sinks when the pier collapses. Kelso drives a motorbike into the ocean and swims to the submarine, where he is captured by the Japanese; undaunted, he declares, "Turn this tub around! You're takin' me to Tokyo!"
On Sunday morning, December 14, Stilwell arrives at the remains of the Douglas home, where most of the other protagonists have gathered. Ward delivers an inspirational speech to those present, vowing that Christmas will not be ruined; to punctuate his point, he nails a wreath to his front door, jarring the unstable house so that it collapses and slides into the ocean. Stilwell mutters, "It's gonna be a long war," and walks away as everyone begins arguing and fighting.

Question: Who informs Wally and Betty about the sub?
Answer: Kelso.