A few months before D-Day, Major Reisman, a U. S. Army officer stationed in England, is given the task of training 12 convicted GI's--murderers, rapists, thieves--for the suicidal mission of parachuting into Nazi-occupied France and blowing up a chateau housing top-ranking German officers. Although the 12 men agree to undertake the assignment in the hope of being granted pardons, their initial reaction to Reisman is one of indifference and contempt. But with Sergeant Bowren's aid, Reisman goads, browbeats, and drives the men until he earns a small measure of respect from each of them. And by standing up for his squad against the opposition of two superior officers, Colonel Breed and General Denton, Reisman eventually succeeds in forging his band of misfits into a fighting unit. To prove the worth of "The Dirty Dozen," a nickname the men acquired when they were deprived of soap and water, Reisman gains permission from General Worden to allow the men to participate in war game maneuvers. After making a fool of the pompous Colonel Breed by capturing his entire staff, the men are given the go-ahead for the dangerous mission. Once parachuted into France, they make their way to the chateau and, by various ruses and surprise attacks, gain entry. Everything goes as planned until one of the Dozen, a Bible-spouting sex degenerate, Archer Maggott, goes berserk and betrays his colleagues. He is shot down, however, as the chateau is turned into a battleground of rapid machine-gun fire and exploding grenades. The savage in-fighting ends only when gasoline-soaked grenades are thrown down ventilator shafts, blowing the chateau to bits. Only three of the 12 men--Wladislaw, Posey, and Sawyer--are still alive when it is over. Both Reisman and Sergeant Bowren are present when General Worden reveals that the ex-criminals who gave their lives are now listed as soldiers who died honorably in the line of duty.