U.S. Marine participation in World War I is known as a defining moment in the Marine Corps' great history. It is a story of exceptional heroism and significant operational achievements, along with lessons learned the hard way. The Marines entered World War I as a small force of seagoing light infantry that had rarely faced a well-armed enemy. On a single June day, in their initial assault "through the wheat" on Belleau Wood against German machine-guns and poison gas shells, the Marines suffered more casualties than they had experienced in all their previous 142 years. Yet at Belleau Wood, Soissons, BlancMont, St. Mihiel, and the Meuse-Argonne the Marines proved themselves to be hard-nosed diehards with an affinity for close combat. Nearly a century later Belleau Wood still resonates as a touchstone battle of the Corps. Two retired Marines, well known for their achievements both in uniform and with the pen, have recorded this rich history in a way that only insiders can. Brig. Gen. Edwin H. Simmons and Col. Joseph H. Alexander recount events and colorful personalities in telling detail, capturing the spirit that earned the 4th Marine Brigade three awards of the French Croix de Guerre and launched the first pioneering detachments of "Flying Leathernecks." Here, hand-to-hand combat seen through the lenses of a gas mask is accompanied by thought-provoking assessments of the war's impact on the Marine Corps.