Marty McFly studied for a Civil War test at Hill Valley College with the assistance of an holographic tutor. Marty went on with playing his guitar with headphones on, ignoring what the tutor was saying. She yelled the date of "February 11, 1864; Chattanooga, Tennessee" within range of the new DeLorean time machine's audio-activated time circuits, enabling the car to change the date and location. Verne Brown upset that he was second to his older brother Jules decided to hop into the DeLorean and take it for a test drive, unaware that the time circuits were activated. Verne drove the DeLorean off the launch pad and broke the time barrier in the sky.
He emerged outside Chattanooga (after the DeLorean was rebuilt with spatial displacement) and was confused by the Confederate Army for some kind of Union Army "devil" wagon. The DeLorean clipped a series of Confederate tents before Verne activated the time machine's night vision. The DeLorean ran into another tent, catching it, and came to a stop. While under the cover of the tent, the car compacted into a briefcase, with Verne to its side.
The armies engage
Verne then encountered Confederate General Beauregard Tannen and his men at the campsite. Tannen asked if Verne was a spy for the Union Army, which he had no answer. Doc Brown, Jules, Marty, and Einstein were forced to take the Jules Verne Train to rescue Verne from the past after finding him in a picture taken of Confederate soldiers a day before the battle, as the text had indicated that the Confederates were wiped out in a massacre the day after the photograph was taken. Doc and Jules were captured by the Union army and Marty and Einstein by the Confederate army.
On the day of the battle, Doc and Jules built an electromagnet from an electric magnetic machine marketed to General Ulysses S. Clayton, and used it to attract all the weapons from both armies. When this failed, Jules was thrown into the middle of the battlefield and Verne came to protect him. When both armies saw this, they stopped and admired the brothers' bonding. Brothers, cousins, and others from both sides began to embrace one another and a truce between Tannen and Clayton was forged.
After the battle was over, the picture in the book changed, indicating that Beauregard's unit never fought in a single battle.
Behind the scenes
There were several battles during the American Civil War known as the Battle of Chattanooga. The battle that inspired the Battle of Chattanooga from Back to the Future: The Animated Series was likely the Battle of Missionary Ridge, which was a battle during the Chattanooga Campaign, that was led by Union general Ulysses S. Grant against confederate general Braxton Bragg.