The Battle of the Somme, which was fought in the Somme river valley in northern France, began on July 1 1916 and was a day of disaster for the British.
Around 100,000 Allied men went over the top to attack the German lines.
By the end of that first day, almost 20,000 British soldiers were dead, making it the worst day in the history of the British Army.
Men from Huddersfield and from across the West Riding fought and died during the Somme offensive.
Local regiments which took part included the Duke of Wellington's, West Yorkshire Regiment, King's Own Yorkshire Light Infantry and the Prince of Wales' Own West Yorkshires.
The 100th anniversary will be marked with events across the country.
Bells will toll for five minutes from 7:30am on Friday, July 1, at churches across Yorkshire and beyond.
Many churches across Huddersfield are taking part and a special civic and community service will be held in Ravensknowle Park at 2pm on Friday, July 1.
How the Battle of the Somme unfolded
July 1 1916
Over 100,000 men go 'over the top' in a disastrous attack on the German lines. A total of 19,240 British soldiers killed on the first and bloodiest day.
July 2 1916
The British attempt to press on, making a series of small attacks over a two-week period. Another 25,000 casualties - killed and injured - on the British side.
July 7 2016
Lists of the Somme dead and wounded begin appearing in local newspapers, including the Huddersfield Daily Examiner. Some Pals Battalions virtually wiped out.
July 14 1916
Around 20,000 British troops attack in the northern part of the Somme. Germans taken by surprise.
July 15 1916
Around 3,000 South African troops fighting on the Allied side take Delville Wood. Heavy losses after German counter-attacks.
July 23 1916
Fighting around Pozieres results in 12,000 Australian casualties.
August 29 1916
German General Falkenhayn replaced by General Hindenburg and his chief of staff Ludendorff. German morale low following 250,000 casualties.
September 15 1916
Tanks unleashed by the British for the first time.
September 17 1916
British efforts hampered by superior German planes. German advance stopped by French artillery and machine guns.
September 25-28 1916
British troops dig-in after taking Morval and Thiepval Ridge.
October 1 1916
British soldiers bogged down in muddy battlefield. Another 57,000 British casualties.
Handmade wooden shrines appear on street corners across the country.
November 13 1916
The British carry out their final battle of the Somme, successfully storming German defences. Around 7,000 Germans captured at Beaucourt.
November 19 1916
The offensives cease and troops dig in. During the 141-day Somme offensive, the British advance seven miles and fail to break the German defence. Despite this, British inflict heavy losses on the Germans.