Germany: Metz-Sablon main station, goods sheds and train hit by 12 DH4s of 55 Squadron (c.90 casualties). Later, 1 Handley Page and 10 F.E.2s (2 lost) attack Thionville (much damage, 35 killed) and Metz-Sablon (night May 17-18).
Western Mediterranean: French convoy escort Ailly sinks UC-35 (destroyed 42 ships worth 65,569t) with gunfire off Sardinia, Germans believe Q-ship the killer.
Ireland: c.150 Sinn Fein leaders arrested for plotting night May 17-18; only Michael Collins and Cathal Brugha escape, but no prosecutions.
Britain: All men born 1898 or 1899 called up. Compulsory meatless day abolished. President of Board of Trade estimates half industry on war work, output below pre-war.