My American born father, who has German ancestry was in World War II. He was one of many men held until their birth certificates could be checked out. People with German heritage like him, along Italians and several other nationalities, were treated this way. I have tried for over 30 years to get information unit info and the like. Over the years bits of information have some, and on occasion I was sent basic medals. But there is still nothing of where in New Guinea he or his unit was. I have heard that J. Edgar Hoover was responsible because of his fear of Germans. It was told to me by another researcher that the records of these military personnel was locked in his office, and thus were not lost in the St. Louis fire. It is surprising how many people do not know about this travesty.
Unsure exactly what information you are looking for, but for information concerning the internment of individuals of German and Italian heritage, it looks like this page at the National Archives might be the spot to start looking.
Immediately after the bombing of Pearl Harbor, President Roosevelt issued Presidential Proclamations 2525, 2526, and 2527 to authorize the United States to detain allegedly potentially dangerous enemy aliens. The FBI and other law enforcement agencies arrested thousands of suspected enemy aliens, mostly individuals of German, Italian, or Japanese ancestry, living throughout the United States.
Some information concerning the internment itself:
By the end of the war, over 31,000 suspected enemy aliens and their families, including a few Jewish refugees from Nazi Germany, had been interned at Immigration and Naturalization Services (INS) internment camps and military facilities throughout the United States. Some of these internment locations included Sharp Park Detention Station, California; Kooskia Internment Camp, Idaho; Fort Missoula Internment Camp, Montana; Fort Stanton Internment Camp and Santa Fe Internment Camp in New Mexico; Ellis Island Detention Station, New York; Fort Lincoln Internment Camp, North Dakota; Fort Forrest, Tennessee; and Crystal City Internment Camp, Kenedy Detention Station, and Seagoville Detention Station in Texas.
This page has numerous links near the bottom which may help guide your research, or provide the records you are looking for. (There are also some sources listed at the end of the Wikipedia article which may also offer some insight)