The title is a play on the 1955 movie Rebel Without a Cause.
The Confederates want to get an "important message" to General Robert E. Lee, but all the carrier pigeons have been shot down. The soldiers realize that Tweety is their last hope and turn to him for their mission. The Union soldiers learn of the Confederates' attempt and counter with their "Messenger Destroyer," who turns out to be none other than Sylvester. "I tawt I taw a damn Yankee tat," says Tweety just before the chase begins.
The bulk of the cartoon uses battle gags, such as Sylvester getting blown out of a cannon; Tweety momentarily tricking Sylvester into thinking Union soldiers are marching to battle (Sylvester tries to confront the canary but is blown away by Confederate soldiers); and Tweety hiding behind cannons on a fighter ship (Sylvester takes the brunt of more explosions).
Eventually, Sylvester disguises himself as General Lee and grabs Tweety. The bird is taken to the firing line for execution. He states that his only regret is that he has "but one wife to give foh my countwy", to which Sylvester says that he has nine lives, But the commander and his soldiers prove incompetent — they shoot Sylvester instead! "It's a good thing I have got nine lives! With this kind of an army, I'll need 'em!"
The version of this cartoon that aired on the former WB Channel cuts out the "damn" in the Confederate Officer's line "Damn Yankees!" and deletes Tweety's line "I tawt I taw a damn Yankee Tat!".
Cartoon Network's version of this cartoon, much like The WB's version, also removes the two usages of the word "Damn". Unlike The WB, however, CN used a fake blackout to end the scene where the Confederate Officer gives his sidekick the letter to deliver to General Lee early to remove the officer's line "Damn Yankees!" and shortened Tweety's line "I tawt I taw a damn Yankee tat!" to "I tawt I taw a Yankee tat!" with a somewhat obvious audio cut. It should be noted that Cartoon Network outside the United States airs the short uncut. 
The version of this cartoon that aired on the syndicated "Merrie Melodies" show left in both uses of the word "damn", but cut a scene in the middle of the cartoon where Sylvester pursues Tweety on a ship and gets blasted by cannons (though this cut scene was shown in a "Hip Clip" on another episode of "The Merrie Melodies Show")
Friedwald, Will and Jerry Beck. "The Warner Brothers Cartoons." Scarecrow Press Inc., Metuchen, N.J., 1981. ISBN 0-8108-1396-3.