Porky Pig is the supervisor of the "Flockheed Eggcraft Factory", where dozens of hens lay eggs for the war effort (in this case, World War II). The hens suddenly get distracted from their egg laying when a handsome rooster named Frankie (who sings like Frank Sinatra) is heard singing outside. Frankie's renditions of "It Can't Be Wrong" by Dick Haymes and "As Time Goes By" (from Casablanca, 1942) causes all the hens to swoon.
Porky rushes to investigate. Soon, he's auditioning for a new crooner; those showing up are caricatures of Vaughn Monroe  ("Shortnin' Bread"), Al Jolson ("September in the Rain"), Jimmy Durante ("Lullaby of Broadway"), Cab Calloway ("Minnie the Moocher", "Blues in the Night"), and Bing Crosby ("When My Dream Boat Comes Home").
Porky asks the Bing Crosby rooster (who introduced himself as "The Old Groaner") to be the crooner, provoking a competition with Frankie. Between the two of them, the overexcited hens' egg production is increased to a level beyond what Porky can handle, including a just-hatched hen chick laying an egg many times her own size.
Surveying literal hills and mountains of eggs all over his farm, Porky was impressed and asks the two roosters, "How did you ever m-m-make 'em lay all those eggs." The roosters demonstrate their technique by crooning at Porky, who lays a mountainful of eggs himself as a result.