Newman, Bernard. The Cavalry Went Through!
Divergence: 1915 CE
What if: A military genius reformed British army training and tactics.
Summary: A British general transforms fighting on the Western Front, knocks the Ottomans of World War I through a different Gallipoli, and then after being made commander of allied forces in the west defeats Germany in early 1917.
Published: Gollancz 1930. V.t. The Cavalry Goes Through!, Holt 1930, Cherry Tree 1939/1940.