- Two spotters in a balloon attached to the Royal Navy ship Manica in the Dardanelles sight a Turkish encampment, fix its position on their map, and telephone the information to the Manica. The ship relays the information to the armoured cruiser Bacchante, which is hidden over the horizon. The Bacchante proceeds to release shells on the encampment, much to the amazement of the unsuspecting Turks. This is the first operational use of a balloon ship during World War I.
- The Ottoman Empire begins to lay siege to the important Armenian cultural, social, and economic city of Van. The Armenians revolt; fighting continues until 17 May.
- German forces under the command of Captain von Kleist retreat from Keetmanshoop in German south-west Africa, surrendering the town to South African forces