What do these writers have in common?

• Ernest Hemingway
• John Dos Passos
• e.e. cummings
• Somerset Maugham
• John Masefield
• Malcolm Cowley
• Sidney Howard
• Robert Service
• Louis Bromfield
• Harry Crosby
• Julian Green
• Dashiell Hammett
• William Seabrook
• Robert Hillyer
• John Howard Lawson
• William Slater Brown
• Charles Nordhoff
• Sir Hugh Walpole
• Desmond MacCarthy
• Russell Davenport
• Edward Weeks
• C. Leroy Baldridge
• Samuel Chamberlain

All drove ambulances during World War I.