The 12th Battalion is a regiment of the Rubinelle Armed Forces and the main faction in the video game Advance Wars: Days of Ruin.
Following the meteor strikes that devastated much of the world, the 12th Battalion, under the command of Captain Brenner, began working to rescue and protect survivors of the strikes.
After saving some settlements from the Beast and his Bandit Raiders, the 12th Battalion found themselves dragged into the war between the Lazurian Army and the New Rubinelle Army, formed by Admiral Greyfield from the remnants of the Rubinelle military after the meteor strikes. Initially siding with Greyfield in exchange for supplies for the civilians the 12th Battalion were protecting, after Greyfield had the Lazurian Commander-In-Chief Forsythe executed and ordered all of the Lazurians to be killed, the 12th Battalion defected from the New Rubinelle Army and helped the Lazurian forces escape.
Declaring the 12th Battalion a traitor, Greyfield sent his forces after them. After Brenner was killed while by Greyfield dropping a nuke on him, Will was appointed the new leader of the regiment to ease tensions between the Rubinelle and Lazurian forces. Under Will's command, the 12th Battalion managed to defeat Greyfield and the New Rubinelle Army.
Brenner's Wolves later went to war with private military contractor Intelligence Defense Systems to claim cure for the Creeper virus, the disease that IDS had used to ravage the 12th Battalion while they were fighting the NRA. After destroying IDS' headquarters, The Nest, the 12th Battalion obtained the cure and returned to camp to administer it
One year after their victory against IDS, Brenner's Wolves had managed to establish a thriving society with the civilians they gathered, figuring out how to grow crops once again.