- Apr 4 Germany protests vigorously to the US, claiming it must insist that Britain lifts its blockade and assert American neutrality
- Apr 5 French begin Woëvre-offensive
Boxing Title Fight
Apr 5 Jess Willard KOs Jack Johnson after 26 rounds to win the heavyweight boxing title in front of 25,000 fans at Oriental Park Racetrack in Havana, Cuba
Jack Johnson
- Apr 14 A's Herb Pennock is within 1 out of pitching 1st Opening Day no-hitter
- Apr 14 Dutch merchant navy ship Katwijk sunk by Germany torpedo
- Apr 14 Turkey invades Armenia.
- Apr 15 Manuel de Falla's ballet "El Amor Brujo" premieres in Madrid
- Apr 15 NY Giant Rube Marquard no-hits Bkln, 2-0
- Apr 18 French pilot Roland Garros is shot down and glides to a landing on the German side of the lines during World War I.
- Apr 19 19th Boston Marathon won by Canadian Édouard Fabre in 2:31:41.2
- Apr 20 The Armenians rise and seize the Turkish town of Van, which they hold until Russians relieve them on 19 May; thousands of Armenians are killed
- Apr 22 1st military use of poison gas (chlorine, by Germany) in WW I
- Apr 22 NY Yankees don pinstripes & hat-in-the-ring logo for 1st time
- Apr 22 The Second Battle of Ypres begins on the Western Front in WW I
- Apr 23 ACA becomes National Advisory Council on Aeronautics (NACA)
- Apr 24 German army fires chloroform gas in Ypres (Leper)
- Apr 24 Leaders of the Armenian community in Constantinople (now Istanbul) are arrested by Ottoman authorities, and many later killed, marking the start of the Armenian Genocide
- Apr 24 Pittsburgh Rebels' Frank Allen no-hits St Louis Terriers (Federal League), 2-0
- Apr 25 First landings at Gaba Tepe and Cape Helles on the Gallipoli Peninsula by ANZAC forces during WWI
- Apr 26 Italy secretly signs the "Treaty of London" with Britain, France and Russia, bringing Italy into World War I on the Allied side
Event of Interest
Apr 27 Counterattack launched by Turkish forces under the command of Mustafa Kemal Atatürk against allied troops
Mustafa Kemal Atatürk