On June 1, 1918, the Battle of Belleau Wood begins. The bloody battle saw Allied troops, particularly personnel of the United States Marine Corps, halting and eventually repelling a German offensive which had been part of the larger Spring Offensive, a final attempt by Germany to win the war before American aid and troops could arrive in full force. Men of the 4th Marine Brigade (including the 5th and 6th Marine Regiments and 6th Machine Gun Battalion), as part of the US Army's 2nd Infantry Division of the American Expeditionary Force (AEF), took up positions to halt a German advance that had broken the French lines. Through weeks of heavy fighting, including hand-to-hand fighting in the forests, the Marines captured Belleau Wood on June 26 as the Germans were forced to retreat.

The Battle of Belleau Wood continues to feature prominently in the legacy, history, and culture of the United States Marine Corps. It was here that the term "Devil Dog" originates from the supposed use of the term Teufelhunde by the Germans to describe the ferocity of the Marines they faced, comparing them to hounds from Hell. The quote "Retreat? Hell, we just got here," also originates from the battle as a reaction to warnings to retreat from the battle and provides the 2nd Battalion, 5th Marines with its motto of "Retreat, Hell." Sergeant Major Dan Daly, then a First Sergeant, is claimed to have uttered the famous words "Come on, you sons of bitches, do you want to live forever?" while encouraging his men to advance.