I just finished reading The AEF Way of War by Grotelueschen. The main thesis was the AEF advocated one particular doctrine and the fighting units, mostly divisions, mainly fought the way they thought best, especially after their first combats. Even when a division espoused the AEF doctrine, subordinate units within the division did it the way they thought best.

It was also an interesting look at group dynamics and leadership. I think it is worth the time.