(This is a more extensive version of an answer I gave to an inquiry about a "trench explosion" on the Western Front. The explosion to which he referred was the dramatic Battle of Messines.) -------- The Battle of Messines (Belgium) on June 7, 1917, was one of the few clear-cut Allied victories of World War I and possibly the greatest example of thorough combat engineering in modern history. The Messines Ridge was directly southeast of the dreaded Ypres sector. The line formed somewhat of a backward "S" curve, as historian James Stokesbury described it; the Allies held the top bulge into German territory, and the Germans held the southern bulge. The line basically followed a ripple of ridges, and as was the case in most of the Flanders region, the Allies held the vulnerable low ground. According to one source, the Allies were taking hundreds of casualties there daily, even when the fighting wasn't "hot." The necessity of taking Messines Ridge was part of an overall plan to break out of the Ypres Salient, push toward the coast, and hook up with an amphibious landing there. The intentions were to encircle the German line leading to the coast, and to take out U-boat bases there. Things didn't quite work out that way, but I'll get to that later. The job of taking the ridge was handed to Gen. Herbert Plumer, a man who was very much admired by his troops; they referred to him as "Daddy." Knowing that he had a number of units comprised of coal miners, he made the decision to attack from beneath No Man's Land by digging a series of mines, packing them with explosives, and detonating them in one massive, devastating blast just before the British and ANZAC troops went "over the top." Mining had been used to some success in other areas, but none matched the intensity that Plumer envisioned. Plumer selected 21 key points along the ridge to mine, stretching from Hill 60 in the southeast corner of the Ypres Salient (a man-made hill 60 meters above sea level, created with spoil from the Ypres-Comines railway cut) and the adjacent "Caterpillar," another man-made hill adjacent to Hill 60, down the line through St. Elois, Hollandasches-Churr Farm, Petit Bois, Maedelstede Farm, Peckham, Spanbroekmolen, Kruisstraat, Ontario Farm, Petit Douve Farm, "Trench 127," Factory Farm, "Trench 122," and ending at Ploegsteert Wood. Tunneling began in 1915. Tunnels -- roughly 100 feet in depth -- ranged from listening galleries in which a man could walk upright, down to smaller shafts in which a man had to work sitting down with a back brace (the troops referred to this as "working at the cross"). Naturally, problems developed. First, all of the blue clay excavated had to be bagged and hauled to rear areas, as German aerial observers might spot the clay and reveal the plan. Second, the Germans knew enough to start countermining; in some cases, mines intersected each other and small battles were fought in the dark. Third, the Germans continually tried to shut down the Allied tunnels by detonating charges on top of them; this, and continuous use of poison gas above, led to a buildup of foul air in the tunnels, and 30-pound breathing devices much like aqualungs were often necessary to work. Despite these problems, mining continued and plans remained the same. When the tunnels reached their target, massive charges of ammonal or gun cotton were planted and wired. Only the mine at Petit Douve Farm was captured and defused by the Germans. The rest remained in place, although no one was certain that they would work properly. After nearly two years of work, the attack was ready to go. It began with a massive shelling that lasted more than a week. In the early hours of June 7, troops were issued cotton to put in their ears, and those in front-line trenches were advised to climb out and lay on top, as the explosions might collapse their trenches. At 03:17, moments after the guns fell silent, the plungers went down. Columns of fire, smoke and debris went flying skyward. The ground itself rippled. One soldier said that for a split second he could see the skeleton of the man in front of him. The captured mine at Petit Douve Farm and two more at Ploegsteert Wood (at the far end of the ridge) did not detonate, but the remaining mines did the trick. Many objectives were captured in a matter of minutes, thousands of dazed Germans surrendered, and the battle was deemed a success. Gen. Plumer received knighthood as a result. The rest of the plan went to hell in a hand basket. The effort to break out of the Ypres Salient is now better known as Passchendaele, one of the Allied low points of the war. With its failure, the amphibious landing never took place. And things pretty much stayed the same at Ypres for the remainder of the war. As a postscript, one of the mines at Ploegsteert Wood did eventually detonate in 1955. Electric towers were erected across the battle some years after the war, and one was placed directly atop that mine. Lightening struck the pole, and the mine went off, leaving a crater 100 feet deep and 300 feet across. The remaining mine at Ploegsteert Wood remains undetonated, and its exact position is now unknown.