|The Battle of Messines was launched on June 7, 1917 by British General Herbert Plumer's second army, which included the 16th (Irish) Division and the 36th (Ulster) Division, near the villages of Mesen (in French Messines, as it was on most maps at that time). The target of the offensive was the Messines Ridge (a ridge running north from Messines village past Wytschaete village, which the Irish Divisions overran, and beyond), a natural stronghold southeast of Ypres, a town in the West Flanders province of Belgium. General Plumer had begun plans to take the Messines Ridge a year before, in early 1916. The attack was also a harbinger to the much larger Third Battle of Ypres, known as Passchendaele, which began on July 31, 1917.|
Over a period beginning more than a year before the attack, the attackers had tunnelled under the German trenches and planted almost 455 tonnes (1,000,000 lb) of ammonal there. A heavy bombardment of the German positions was initiated and then halted. The defenders returned to their positions expecting an assault to follow. The detonation of the explosives all timed for 3:10am, killed approximately 10,000 German soldiers. It said to have been heard as far away as London and Dublin, and was possibly the loudest man-made noise made up to that date. In Switzerland the explosions registered as an earthquake. The real attack then followed.
Not all of the explosives went off. Two of the original 21 mines failed to ignite due to one reason or another. On July 17, 1955, a lightning strike set off one of the remaining mines, the only casualty being a dead cow. The 21st mine is believed to have been found in recent years, but no attempt has been made to remove it. Several large water-filled craters still mark the original positions of the German trenches.