By war's end the American Expeditionary Force had progressed along a bloody learning curve, developing sophisticated techniques—small flexible formations, fire-and-maneuver and infiltration—for breaking the trench warfare stalemate. Eventually, the AEF integrated new weapons like poison gas, tanks and aircraft into its offensive tactics and pioneered the mechanized combined arms warfare still practiced by the U.S. Army. The exploits of the Fifth "Red Diamond" Division exemplify this critical period of development.