During the war he fought alongside other U.S. Marines in the German Offensive of 1918 and in the Battle of Belleau Wood against German Empire troops that same year. The battle is seen as an important success for allied forces against the Germans. On the night of 4 June, Lt. Eddy, the intelligence officer for the 6th Marines, and two men stole through German lines to gather information about German forces. They gathered valuable information showing the Germans were consolidating machine gun positions and bringing in artillery. While this activity indicated an attack was not immediately likely, their increasing strength was creating a base of attack that raised concern about them breaking through to Paris. Eddy was wounded in his right hip at Belleau Wood. The hip eventually became infected, which led Eddy to lose all mobility in the hip and left him with a pronounced limp for the rest of his life. He was then sent back to the U.S. to recuperate.