The plan was the work of the German army chief-of-staff Alfred von Schlieffen.
It took nine years to devise - it was started in 1897, presented in 1905, and revised in 1906.
The plan imagined a huge hammer-blow at Paris, using 90 per cent of the German army, swinging down through Belgium and northern France, to take out France in a quick, decisive campaign.
It was a plan of attack - for Germany, mobilisation and war were the same thing.
It was Germany's only plan for war.
It did not plan for a situation where Germany was at war with Russia, but not with France. When the German chancellor Bethmann-Hollweg asked "Is the Fatherland in danger?", the German general Moltke declared "Yes".
In the event, Russia took only ten days to mobilise, and Moltke was forced to send some troops to the eastern front, which weakened the main attack on Paris.
When the German army asked permission to go through Belgium on 2 August 1914, the Belgians refused, so the German army had to fight its way through Belgium. This slowed it down and tired the soldiers.
Britain's decision to uphold the 1839 Treaty with Belgium amazed the Germans. "For a scrap of paper, Great Britain is going to make war?" said the amazed Bethmann-Hollweg.
In the event, the British Expeditionary Force (BEF) arrived to resist the Germans, and held them up at the Battle of Mons on 23 August 1914. With his army exhausted and many of his best forces killed, Moltke was defeated at the battle of the Marne on 6-10 September 1914. "Sir, we have lost the war," he told the Kaiser.