Q. My Grandfather/Father/Uncle* fought in Normandy/Phillipines/Italy/Ulan Bator** with the 542nd/51st/12th** where do I find information about him and his unit?
A. If they died in action then sites such as the Commonwealth War Graves Commission www.cwgc.org/ will allow you to search their records.
The Military Indexes web site has many useful links for research.
*Delete as appropriate **or something similar