| Manufacturer | Designation | nickname |
|---|---|---|
| Curtiss | O-1 | Falcon |
| Loening | O-1 | |
| Douglas | O-2 | |
| Douglas | O-5 | |
| Thomas-Morse | O-6 | |
| Douglas | O-7 | |
| Douglas | O-8 | |
| Douglas | O-9 | |
| Curtiss | O-11 | Falcon |
| Curtiss | O-12 | |
| Curtiss | O-13 | |
| Douglas | O-14 | |
| Keystone | O-15 | |
| Consolidated | O-17 | Courier |
| Curtiss | O-18 | |
| Thomas-Morse | O-19 | |
| Thomas-Morse | O-20 | |
| Thomas-Morse | O-21 | |
| Douglas | O-22 | |
| Thomas-Morse | O-23 | |
| Douglas | O-25 | |
| Curtiss | O-26 | |
| Fokker | O-27 | |
| Vought | O-28 | |
| Douglas | O-29 | |
| Douglas | O-31 | |
| Douglas | O-32 | |
| Thomas-Morse | O-33 | |
| Douglas | O-34 | |
| Douglas | O-35 | |
| Douglas | O-38 | |
| Curtiss | O-39 | Falcon |
| Curtiss | O-40 | Raven |
| Douglas | O-43 | |
| Douglas | O-46 | |
| North American | O-47 | |
| Stinson | O-49 | Vigilant |
| Bellanca | O-50 | |
| Ryan | O-51 | Dragonfly |
| Curtiss | O-52 | Owl |
| Stinson | O-54 | Voyager |
| Erco | O-55 | |
| Lockheed | O-56 | Ventura |
| Taylorcraft | O-57 | Grasshopper |
| Aeronca | O-58 | Grasshopper |
| Piper | O-59 | Grasshopper |
| Kellett | O-60 | |
| Stinson | O-62 | Sentinel |
| Interstate | O-63 | Grasshopper |
| Consolidated | O-17A | Courier |