The Battle of the Somme ran from July 1st until November 18th, 1916. It was the largest battle of the First World War on the Western front, and cost over a million casualties. It's considered to have been one of the bloodiest battles in human history.
The Telegraph sums it up:
The first day of the 141-day campaign, July 1 1916, was and still is the deadliest day in the history of the British Army. Almost 20,000 British Empire soldiers lost their lives in just 24 hours.
. . .
The battle was planned to end months of deadlock on the Western Front, break through Germany lines and also relieve pressure on the French forces at Verdun - a nearby town that had been under siege.
Laden with heavy kit, the British infantry began their laborious advance at 7:30am on July 1 following a week of intense artillery bombardment of German positions from the village of Serre to Maricourt which had intended to annihilate enemy forces.
There was a belief that following this bombardment, troops would take a safe stroll across no-man's land to trenches the Allies thought would be empty, but German defences were far better than they had anticipated.
German troops had hidden safely in deep dugouts during shelling the previous week and emerged quickly, catching the Allies by surprise and shooting them down in vast numbers.
In the first 24 hours, there were 57,470 casualties (including 19,240 men killed) – just under half the total engaged. Most men were killed in the first few minutes.
The Battle of the Somme continued for another 140 days as Britain's attempts to consolidate its gains quickly degenerated into a series of bloody piecemeal fights for scraps of wood and village.
After the opening assault, the next major set-piece attack was at the Battle of Flers-Courcelette in September, known as the debut of the tank in modern warfare. The last major battle was at the Ancre in October.
On both sides ill-prepared and poorly-equipped units were thrown into the fight, causing terrible casualties, including an average British casualty rate of 3,000 a day.
Finally winter weather brought it all to a sodden halt and the Battle of the Somme officially ended on November 18. The net gain was a strip of land 20 miles wide and six miles deep.
There's more at the link.
Here's a BBC documentary about the battle. I highly recommend watching it in full-screen mode.
The Somme battlefield is still riddled with mines, shells, bombs, grenades and firearms covered by mud during the fighting. 25 tons of munitions have already been collected this year alone, and it's estimated it'll take another 500 years to remove them all.
The battle also marked the offensive debut of the so-called 'Pals battalions'. Raised by Lord Kitchener, these comprised men from a single district or community. Unfortunately, this meant that if one of them suffered heavy casualties, it had a disproportionate impact on the area it came from compared to a 'normal' battalion, which drew its manpower from across the country, so that its casualties didn't impact one region in particular. For example, the town of Accrington and its surrounding area lost 303 men killed and 281 wounded out of the 720 it had contributed to its Pals battalion - a casualty rate of over 80%. The town never fully recovered from so devastating a loss, which is still commemorated. After the Battle of the Somme, some of the Pals battalions were disbanded and their personnel distributed to regular battalions, while others received replacements from a wider geographical area, to avoid a repetition of such a calamity.
I think Eric Bogle has summed up the Battle of the Somme better than most.
May those who died there rest in peace.