AUSTRIAN TRENTINO OFFENSIVE begins on 21-mile front with 4 hours intensive barrage from 0600 hours. Elite XX Edelweiss Corps (Archduke Charles) has 253 guns in direct support plus 140 from III Corps, captures Costa d’Agra and Mt Coston (5,745 ft) breaking Italian first line until next day, but VIII Corps to West fought to a standstill by Roma Brigade and Alpini; as is XXI Corps though XVII Corps secures parts of Armentera Ridge (4,954 ft) in eastern diversion along Val Sugana that Pecori-Giraldi mistakes as main threat.
Artois: British mine and storm 250 yards trenches on Vimy Ridge but Germans take crater on May 17.
Middle East and Sea War
Arabia: Allied blockade of Hejaz coast begins.
Britain: Foreign minister Grey states Allies fighting for a free Europe. Bethmann replies on May 23 that Germany will make peace on basis of security against attack.
Belgium: Gouverneur-General Bissing decrees unemployed will accept work for Germany.
Ireland: Casement charged with high treason for Easter Rising.