Paths of Glory - Book vs. Movie

 Although Humphry Cobb's 1935 novel been adapted into a Broadway play,  Kubrick's 1957 film was the first  -and only - movie adaption.  I may write in more detail, but for now I'll just summarize the differences as follows:

The Expanded Role of Col Dax  

In the novel, Col Dax is just one of 8 main characters and pretty much disappears after the decision to go ahead with the Court Martial.  He's regular army officer, not a lawyer. Given that his producer and box office star Kirk Douglas was playing the part, Kubrick had to expand the role. So Kubrick and Harris (his co-screenwriter) did the following:

• Movie Dax was changed to a Reserve Office and prewar defense lawyer.  This allows Movie Dax to become the defense lawyer at the Court martial.  The  novel's Captain Etienne is eliminated. 
• Movie Dax leads the attack on the anthill. In the novel, the attack is headed a Major, the Battalion commander. Further,  Movie Dax takes over the roles of several other inferior officers. Douglas orders Roget to go on patrol and receives his report.  Later, Douglas orders Roget to head the firing squad and also tells the sergeant to let them stay in the Cafe for a while. The Regiment seems to be run by Douglas personally. 
• Kubrick adds a subplot related to the general ordering a barrage on his own troops.  The artillery officer gives Movie Dax a written statement saying so.  Douglas then confronts Adolphe Menjou  and demands the men be freed or else.  Later, Menjou offers Douglas a Generalship which Movie Dax turns down in a burst of anger.  None of this is in the novel - which ends with the execution.  Further, in the novel, the artillery officer says nothing, since he never fired on the troops and received no written orders. 

Other Changes

• The film makes the attack seem more dramatic. In the novel, nobody can advance behind the French wire, the Germans' lay down a barrage and machine gun fire and prevent any forward movement.
• The closing café scene is pure Kubrick
• The Characters of General Assolant (Macready) and De Guerville (Menjou) are made more deranged and sinister. In the novel, the attack has been ordered by Joffre and is considered a necessary prerequisite to the upcoming General offensive. An "assault division" is required. so Assolant is given the job.  Assolant protests his Division is tired and understrength but eventually agrees since he's a "fighting General".  The same is true of Col Dax.  He protests, but he's regular army and orders are orders. 
• The General's chit chat with the soldiers was added by Kubrick.  As is the slapping of a soldier for shell shock. 
• Kubrick makes Col Dax into a liberal civilian in uniform,  Movie Dax calls Menjou a "degenerate old man"  and tells Macready "Patriotism is the last refuge of the Scoundrel".  In fact Douglas is so contemptuous of patriotism and the military you wonder why he's in the army.
• Kubrick shows Ralph Meeker as an innocent victim. In the novel, his character tries to shoot Lt. Roget while on patrol
• In the novel, the prisoner who attacks the Priest has his leg broken by the guards. Kubrick changes this to Ralph Meeker hitting the man on the head.  Later, Kubrick shows the Priest comforting a soldier on the way to the execution. I suppose this was soften the attack on the Priest.