The Jens H. F. B. Neergaard you are asking about is my 2nd great grandfather on my mothers side. He was born in the area of northern Germany or Southern Denmark that was constantly fought over. Our family stories say he was a supporter of the cause of black americans and that he fought for the north and that he died in a prison camp. I too have looked in vain for any information on his military records and can find nothing. His son my great grandfather rode horse back from to Tenn. to Washington territory and was an early pioneer in that state. I was born there. Wish I could help.