Looking for my husband father

I am trying to find my husband's father that was in Vietnam sometime during 1971-1972,he had 1 son and was there when he was born and took care of my mother in law,he left to come back to America and she had my husband in Dec 1972.His father wrote many letters but my mother in law never answered back,my husband looks alot like his Dad,cause he got to see pictures of him when he was younger but they all had to be destroyed,they lived near Saigon with their grandmother until he was older.all I know is he was on a ship and might have been called Ed or Craft and was from CA,if anyone has any information or knows how we can get any information or DNA testing,please send me an email.Thank You.