- US President Woodrow Wilson threatens to sever diplomatic ties with Germany following the sinking of the British passenger ferry SS Sussex in the English Channel by UB-29. The German government later responds with The Sussex Pledge, agreeing to give adequate warning before sinking merchant and passenger ships. The pledge is upheld until February 1917, when unrestricted submarine warfare resumes.
- General Vladimir Liakhov’s Russian forces occupy the city of Trebizond on the shores of the Black Sea, abandoned three days earlier by the Turks
- Turkish troops counter-attack the British at Sannaiyat in Mesopotamia, regaining 500 yards of territory
- Russian forces continue their progress west of Erzerum in Turkey
18 April 1916
