Tim Heap climbed into the twisted carcass of Deborah, a British tank that smashed through German defences precisely 100 years ago in the battle that marked the birth of modern warfare.

"My grandfather would have been standing right here up front. His DNA is in still inside. And if he had got out 30 seconds later, I wouldn't be here," said the 65-year old retired lecturer.

At dawn on November 20, 1917, an armada of almost 500 British "land ships" emerged from the mists to wage the Battle of Cambrai, northern France, the first in history where tanks were used en masse with air support.