Battlefield debut of French Renault FT-17 light tank: 30 (3 lost) in Retz Forest helps stem German advance as do 4 more divisions. During May 250,000 US troops sail for France, record of 9 divisors land.
Atlantic: Empty US transport President Lincoln sunk by U-90.
North Sea: British destroyer Fairy (convoy escort) sinks after ramming and destroying UC-75.
During May Allied and neutral shipping lost to U-boats: 112 ships (59 British with 407 lives lost) worth 294,019t (192,432 British including ship mined). U-boat figure 139 ships worth 296,558t including most successful 1918 month in Mediterranean, 56 ships worth 122,7175t of which 12 (9,923t) to Austrians. Record of 14 U-boats sunk (3 in Mediterranean).
Western Front: Air-to-air combat over river Aisne costs 12 German and 17 French aircraft. Lieutenant Duncan Campbell (94th Aero Squadron) becomes first American air arm ace with his 5th victory. Total Allied May losses 362 aircraft and 24 balloons. German non-combat loss 175 aircraft and 201 in action.
Germany: 10 RAF D.H.4s (lost) bomb Karlsruhe (78 casualties) and stop factory production for 1 hour.
Turkey: Great 27-hour fire at Constantinople causes 520,000 Turkish Pounds damage. Maximum prices abolished, trade made free.
Britain: War Savings certificates reach 2 million. In May Labour Ministry creates Appointments Department for officers. May’s 197,274t new merchant shipping a record.
Belgium: Cooreman succeeds Baron de Broqueville as Prime Minister.
USA: War Secretary can conscript conscientious objectors for unpaid farm work.
France: Paris munition plants: ‘Morale of the workers is excellent’.