The First World War was a conflict of attrition with neither side able to gain much of an advantage.
But below the battlefields of the Western Front a secret war was going on. This one involved many men from the North East
Desperate to gain an advantage and break German front lines, Lord Kitchener formed tunnelling companies.
They were made up largely of miners who had joined the war effort to get a break from the rigours of the coal face. But they quickly found themselves deep underground. The skills they brought with them proving invaluable.
The role of the miners was to dig tunnels under the German front lines and plant explosives. The Germans also had tunnelling companies, and both sides often found themselves deep underground often just a few yards apart, separated by nothing more than a wall of earth.
Lochnagar Crater, at La Boiselle, on the Somme is perhaps one of the best surviving examples of the impact that miners had.
This huge crater is 90 feet wide and 70 feet deep. It was created by 60,000lbs of explosives.
This was detonated on the first day of the battle of the Somme. The explosion rose 1,200 metres into the air.
Watch Kenny Toal's report here