WHEN William Bentley witnessed what was then the biggest man made explosion of all time, it marked the success of a mission he was never to forget,

For he was the messenger who passed on the order from headquarters to blow up Messines Ridge during the Battle of Passchendaele, one of the bloodiest encounters of the First World War.

And when the front line general acted on the directive, the result was carnage among the German forces.

Interviewed in the fifties by the NDT, William, of Blackburn Street, Blackburn, explained: "I had only gone half way from the front line back to headquarters, when the plunger was pressed and the whole earth seemed to shake.

"Terrific shock waves threw the British troops off their feet and they watched in awe as the dark mass of the ridge rose skyward."

He served in the 7th Battalion East Lancashire Regiment, 19th division - one of the finest in the British Army, bar none, he declared - and, at the age of 21, was soon engaged in the bitter conflict.

He was one of 32 runners who took messages between the companies in the trenches and the officers at hq - and was one of only two who lived to tell the tale.

"I was given the message to blow up the ridge, both verbally and on paper," he recalled later "and all the way to the front line I was dodging into dug outs and along communication trenches, where sappers were pumping out water."

William delivered the fateful note to General Gough, who urged him to get away as far as possible, but had only gone half way when the ground began to shake.

He remembered: "The explosion rocked me on my feet and pieces of earth six feet square were flung up in the air."

William had earlier helped to dig tunnels into the ridge, some 2,000 feet long, which were then packed with nearly a million pounds of explosives.

The enemy, however, had a similar plan and were themselves tunnelling under British held territory.

During the conflict, William was hit by a sniper's bullet, but after a brief convalescence was back in the front line trenches, though he said: "The day I took the message to press the plunger and sent the Messines Ridge sky high, was the roughest job in the war. I'll never forget it."

* Starting from 3.10 am on June 7, 1917, the various mines at Messines were fired within the space of 20 seconds.

The joint explosion ranks among the largest non-nuclear explosions of all time and surpassed the mines which had been fired on the first day of the Somme 11 months before.

The sound of the blast was considered the loudest man-made noise in history and it killed, it is believed, around 10,000 German soldiers.