France: FIRST US TROOPS DISEMBARK (1,308 US soldiers by May 31).
Champagne: Three German counter-attacks fail.
Isonzo: Italian 4th Division occupies ruins of Kostanjevica village but Austrian guns force evacuation. Italians capture 10 guns and reach river Timavo taking 800 PoWs but Hill 28 (Major Randaccio dies in poet D’Annunzio’s arms) not secured (until May 27).
Western Mediterranean: British hospital ship Dover Castle (7 lost) sunk by UC-67 (Neumann) off Algeria, but destroyer escort gets wounded off. (Neumann acquitted at June 1921 Leipzig War Crimes Trial on higher orders defence.)
Channel: Heinkel designed Brandenburg seaplane fighters shoot down a formation of 4 French Navy FBA flying boats.