Let me see, the first unit I with was the 4th ID. It fought in WWI in the Aisne-Marne Operation, the Vesle Sector (Champagne), occupied the Toulon Sector (Loraine), St-Mihiel Operation, and the Muese-Argonne Operation.
In WWII they came ashore at Utah Beach on D-Day, St.Mere Eglise, Crisbecq and Azeville, Joganville, occupied Cherborg, St. Pois, participated in the liberation of Paris, Muese and Biever Rivers, Siegfried Line at the Schnee Eifel ridge, Huertgen Forrest (had an uncle that lost an eye to a sniper here), The Battle of the Bulge, Fuhren, the Siegfried Line, crossed the Rhine River into Germany, crossed the Danube into the Miesbach-Gustieg area and was relieved by the 101st Airborne Division.
During my time with the division, it served in Vietnam. The division fought in there through December 1970, earning eleven campaign streamers for its colors in 5 years. But that's a whole other story.
That's the fifty cent tour.
http://www.army.mil/CMH/matrix/4ID/4ID-WSvc.htm