I'm assuming, of course, that the place was built after the war. I don't know if armies already keep some fields for veterans, specially because you don't know how big the war would be, and if you can bring all the bodies back.
I know very little of American History, but I got curious in this aspect, I hope someone knows!
I haven't see it in a while, but I'm pretty sure the grandpa is at the cemetery near Colleville-sur-Mer, in Normandy, France. It was established in June 1944 by the American First Army (called St. Laurent then) as a temporary place to inter the dead of the invasion. The current spot was dedicated in 1956, I believe, and was granted to the US by France in perpetuity. It is maintained by the US, mostly by servicemen/women. About 10,000 soldiers are buried there, mostly those who lost their lives during the invasion of Normandy or the following operations. This was standard for combat zones in WW2, but after the war many of the identified dead were exhumed and brought back to the United States. In special cases, at particularly meaningful locations, the dead were left as a memorial of their sacrifice and the enormity of the event. Normandy is one such case. Another, sort of, would be the sailors on the submerged USS Arizona, at Pearl Harbor.