Christen Andersen the Musteteer

I have been trying to find the records of my gt gt grandfather Christen Andersen. He didn't marry my gt grandfather Anders Christen Christensen's mother. But Anders C Christensen, born 19th Dec 1839, was confirmed 1 oct 1854 at the Vestre Aker church and he is described as living at 'Holmen Farm' and being the son of Randine Pedersdatter [unmarried] and Musketeer Christen Andersen. He was a military man of some sort, born at Oslo about 1812. I have no idea where to search for his military records. We think he later married Lisbet Knudsdatter about 1841. Without the marriage of Anders'parents it has proved very difficult to find Christan Andersen's birth at Christiania [Oslo]. Any help would be appreciated.