I don’t know of any.
My grandfather was in the military, but that was between WW1 and WW2, so he never saw any action.
Just about all of my uncles (and my Dad) would have been of age to serve during Vietnam, but none of them did.
I imagine I have ancestors who fought in the Civil War, but nothing confirmed.
Another who has no known family member KIA, or for that matter fought in any war or skirmish of this century or the last.
On the other hand I had ancestors on both the Jacobite and Royalist armies at Culloden (1745), which disqualifies me.
No direct ancestors in the 20th century killed in battle that I know of. I lost several close friends in Vietnam. My father had 13 brothers who I think 10 served in world war II or Korea. A couple of purple hearts.
Bros! Ditto that for my family on Dad’s side. Alsace-Lorraine, then Russia, then Canada and down to Kansas. Mom’s side has been mucking about the South since Jamestown, but managed to avoid getting killed in battle.
I don’t know of any in my family. I think my paternal grandfather and both of my maternal grandparents were in WWII, and survived - not quite sure what their exact jobs were, maybe nothing too dangerous.