June 7-10, 1917 – Australian, New Zealand and British troops attack Messines Ridge, near Ypres in Belgium.
The offensive at Messines force the Germans to move reserves to Flanders from the Arras and Aisne fronts, which relieves pressure on the French. The tactical objective of the attack at Messines is to capture the German defences on the ridge, which run from Ploegsteert (Plugstreet) Wood in the south, through Messines and Wytschaete to Mt. Sorrel, to deprive the German 4th Army of the high ground south of Ypres.
The battle is heralded by the explosion of 19 great mines beneath the German lines (several craters can still be seen today). In what is considered the finest attack of the war to date, the Germans are swept off the ridge, and the stage is set for the enormous British advance later in the year.