| Under the Liberty Tree: A Story of The 'Boston Massacre'
James Otis | |
| Under the Lilacs
Louisa May Alcott | |
| Under the Maples
John Burroughs | |
| Under the Mendips: A Tale
Emma Marshall | |
| Under the Meteor Flag: Log of a Midshipman during the French Revolutionary War
Harry Collingwood | |
| Under the Mikado's flag
Edward Stratemeyer | |
| Under the mizzen mast: A voyage round the world
Nehemiah Adams | |
| Under the Ocean to the South Pole; Or, the Strange Cruise of the Submarine Wonder
Roy Rockwood | |
| Under the periscope
Mark Herbert Joseph Bennett | |
| Under the Polar Star; or, The Young Explorers
Dwight Weldon |
