It's December of 1941, and the people of California are in varying states of unease, ranging from a sincere desire to defend the country to virtual blind panic in the wake of the Japanese attack on Pearl Harbor. Thus begin several story threads that comprise the plot of this strange period comedy, a sort of satirical disaster movie, from Steven Spielberg.
The stories and story threads involve lusty young men, officers (Tim Matheson) and civilians (Bobby Di Cicco) alike, eager to bed the young ladies of their dreams; Wild Bill Kelso, a nutty fighter pilot (John Belushi) following what he thinks is a squadron of Japanese fighters along the California coast; a well-meaning but clumsy tank crew (including John Candy) led by straight-arrow, by-the-book Sgt. Tree (Dan Aykroyd), who doesn't recognize the thug (Treat Williams) in his command; and homeowner Ward Douglas (Ned Beatty), who is eager to do his part for the nation's defense and, despite the misgivings of his wife (Lorraine Gary), doesn't mind his front yard overlooking the ocean being chosen to house a 40 mm anti-aircraft gun.
There is also a pair of grotesquely inept airplane spotters (Murray Hamilton, Eddie Deezen) who are doing their job from atop a ferris wheel at a beachfront amusement park; a paranoid army colonel (Warren Oates) positive that the Japanese are infiltrating from the hills; a big dance being held on behalf of servicemen, being attended by a lusty young woman of size (Wendie Jo Sperber) eager to land a man in uniform; and General Joseph Vinegar Joe Stillwell (Robert Stack), in charge of the defense of the West Coast, who can't seem to get anyone to listen to him when he says to keep calm.
And, oh yes, there's also a real Japanese submarine that has gotten all the way to the California coast under the command of its captain (Toshiro Mifune) and a German officer observer (Christopher Lee), only to find itself without a working compass or usable maps.
Its captain won't leave until the sub has attacked a militarily significant, honorable target, and the only one that anyone aboard ship knows of in California is Hollywood.
By New Year's Eve, all of these characters are going to cross paths, directly or once-removed, in a comedy of errors and destruction strongly reminiscent of the finale to National Lampoon's Animal House (as well as several disaster movies from the same studio), but on a much larger and more impressive scale.