Books about War stories (sorted alphabetically)
- Norma Kent of the WACS Roy J. Snell
- No Sons Left to Die! Hal Annas
- Number 70, Berlin: A Story of Britain's Peril William Le Queux
- Off Santiago with Sampson James Otis
- Okewood of the Secret Service Valentine Williams
- Old Mortality, Complete Walter Scott
- Old Mortality, Volume 1. Walter Scott
- Old Mortality, Volume 2. Walter Scott
- One Man's Initiation—1917 John Dos Passos
- One of Ours Willa Cather
- Onslaught from Rigel Fletcher Pratt
- On The Blockade Oliver Optic
- On the Irrawaddy: A Story of the First Burmese War G. A. Henty
- On the Plantation: A Story of a Georgia Boy's Adventures during the War Joel Chandler Harris
- Operation Lorelie William P. Salton
- Oswego-joella: "Tienviitan" seikkailuja, intiaanikertomus (Finnish) James Fenimore Cooper
- Our Town Jerome Bixby
- Out of the Dark Nebula Milton L. Coe
- Outpost on Io Leigh Brackett
- Pathfinder; Or, The Inland Sea James Fenimore Cooper
- Path of the King John Buchan
- Patty—Bride Carolyn Wells
- Peace Norman Arkawy and Stanley Henig
- Pilot: A Tale of the Sea James Fenimore Cooper
- Pretty Quadroon Charles L. Fontenay