| Soldier Name | Regiment & Company | Rank I/O | Alternate Name | Comments |
| O. H. Combs | 21st Reg’t, MS Inf Co E | Pvt/" | Combs, Oliver C. | |
|---|---|---|---|---|
| O. P. Comer | Wright's Reg’t, AR Cav Co K | Pvt/" | Conor, O.P. | |
| Olin Coombs | 89th Reg’t, OH Inf Co F&S | Pvt/QMSgt | ||
| Olin Cooms | 89th Reg’t, OH Inf Co F&S | Pvt/QMSgt | Coombs, Olin | |
| Oliver Combs | 71st Reg’t, IL Inf Co I | Pvt/" | ||
| Oliver C. Combs | 21st Reg’t, MS Inf Co E | Pvt/" | ||
| Oliver M. Combs | 3rd Reg’t, CA Inf Co C,A | / | Combs, Oliver K. or Coombs, Oliver M. | |
| Oliver M. Coombs | 3rd Reg’t, CA Inf Co C,A | Pvt/" | ||
| Oliver T. McComas | 94th Reg’t, IL Inf Co I | Pvt/" | McComas, O. | |
| Oliver T. McComas | 37th Reg’t, IL Inf Co G | Pvt/" | ||
| Orange McComber | 8th Reg’t, NY Cav | Pvt/ | McCumber, Orange | |
| Oren McComb | 1st Reg’t, Eng’rs & Mechs, MI Co G | Pvt/" | ||
| Orlando Macomber | 1st Reg’t, VT Heavy Art Co K | Pvt/" | ||
| Orrion McComber | 3rd Reg’t, NC Inf Co D | Pvt/" | McCumber, Orrin | |
| Oscar Combs | 48th Reg’t, NY Inf Co B | Pvt/" | ||
| Oscar Coombs | 15th Reg’t, ME Inf Co H | Pvt/" | Coombs, Oscar A. | |
| Otis Macomber | 76th Reg’t, NY Inf Co B | Pvt/" | ||
| Otis McComber | 16th Reg’t, ME Inf Co K | Pvt/" | ||
| Otis McComber | 147th Reg’t, NY Inf Co A | Pvt/" |