Was your ancestor a military veteran?
The 1910 & 1930 Federal Census Population Schedules have questions regarding previous military service.
1910 #30.....Military, survivor of Union or Confederate Army or Navy.
1930 #30......Military, veteran (Y/N)
#31..............War or Expedition (CW,SA,WW)
If the answer is affirmative to these questions a search of military records would seem to be in order.
Art Thomas