It was 100 years ago today that Britain declared war on Germany and the First World War began.

One of the deadliest conflicts in history, the war mobilised more than 70 million military personnel from around the world and in Britain, thousands raced to enlist when war was declared on August 4, 1914.

Today commemorative services and parades across the UK have been held to mark the important date, while the Duke and Duchess of Cambridge attended a special service in Belgium to mark the 100th year anniversary of the outbreak of war.

Click below for pictures of events held to mark the centary of World War One

To commemorate the 100th anniversary of the outbreak of the First World War, here's 20 facts about the so-called 'war to end all wars':

  1. The First World War claimed the lives of eight million soldiers, with many more left physically and mentally damaged. In addition, nine million civilians were killed.
  2. On the Western Front - which stretched 440 miles from the Swiss border to the North Sea - 300,000 houses, 6,000 factories, 1,000 miles of railway and 112 coal mines were destroyed.
  3. The Battle of the Somme, which raged from July-November 1916, was one of the bloodiest battles humanity has ever seen, with the British suffering 60,000 casualties on the first day.
  4. When the Battle of the Somme ended in November, the British had suffered 420,000 casualties, the French 195,000 and the Germans around 650,000.
  5. When war was first declared, many believed it would be over quickly - the Observer newspaper declared in August: "Six months should see the end of it".
  6. World War One sparked the invention of plastic surgery -  surgeon Harold Gillie pioneered early techniques of facial reconstruction after being horrified by shrapnel injuries, where shards of twisted metal could easily rip a man's face off.
  7. British Field Marshal Douglas Haig - commander of the Battle of the Somme - set up the Poppy Appeal in 1921. The first appeal raised £106,000 (nearly £30 million in today's terms) and all the poppies were supplied from France.
  8. The First World War also led to the creation of blood banks after the British Army began the routine use of blood transfusion in treating wounded soldiers. A US army doctor, Captain Oswald Robertson, established the first blood bank on the Western Front in 1917.
  9. A huge explosion on the French battlefield was so loud it was heard by the Prime Minister in London. Miners dug secret tunnels up to 100ft underground to detonate mines beneath enemy trenches - their biggest success was at the Messines Ridge in Belgium, where more than 900,000lbs of explosives were detonated across 19 tunnels - and the explosion was heard in Downing Street.
  10. Around 12 million letters were delivered to the front every week - by the end of the war, two billion letters and 114 million parcels had had been delivered.
  11. More than 250,000 underage British soldiers fought in the First World War - recruits had to be 18 to sign up and 19 to serve overseas, but as most people didn't have birth certificates, it was easy for underage boys to lie about their age.
  12. To enlist as a solder, men had to be at least 5ft3ins, with a minimum chest size of 32 inches - so a well built 16 year old was likely to be allowed to enlist. However one in five were sent home within a month, after confessing their real ages or being considered too small to fight.
  13. World War One opened up the world of work to British women, with around two million women replacing men at their jobs.
  14. Women worked on the land, on public transport and in clerical roles in post offices - but the largest area women worked in was the munitions factories, making gun shells, explosives, aircraft and other war materials.
  15. The British war machined produced four million rifles, 250,000 machine guns, 52,000 aeroplanes, 2,800 tanks, 25,000 artillery pieces and over 170 million rounds of artillery shells by 1918.
  16. By the end of the war there were more than 10,000 nurses in the Queen Alexandra's Imperial Military Nursing Service. The first hospital staffed entirely by women, Endell Street Military Hospital in Covent Garden, London, was opened in May 1915.
  17. More than one million horses and mules were deployed by the British during the war - there were not enough to meet demand in Britain, so more than 1,000 per week were shipped over from North America.
  18. Around 20,000 dogs served as messengers in World War One - mainly family pets donated to the war effort or strays taken from pounds. However soldiers developed bonds with the animals and often offered to deliver messages in their place.
  19. It is estimated around 325,000 men suffered shell shock during the First World War - resulting in specialist hospitals, like Craiglockhart in Edinburgh, being established to try and treat the condition.
  20. Journalists risked the death penalty during the war - legislation passed in 1914 allowed the War Office to censor the press and threatened the death penalty for any reporter convicted off assisting the enemy. Some reporters were embedded with the British Army - others lived as fugitives in France.

Services across Huddersfield have remembered the fallen of the First World War:  click here for photos, video and to read more.