May 23 (Thur.)
Costa Rica declares war on the Central Powers.
The British armed merchant cruiser Moldavia, while transporting American troops, is sunk by a submarine in the English Channel (56 lives lost).
May 24 (Fri.)
Mesopotamia:—The British withdraw from Kirkuk (see May 7 and Oct. 25).
May 26 (Sun.)
The Italians capture the Monticello Pass (in the Adamello district) with 870 prisoners and 12 guns.
The British transport Leasowe Castle is sunk by a submarine in the Mediterranean (92 lives lost).
May 27 (Mon.)