PARIS - Even for the darkest of pessimists, when the great powers of Europe went to war in the summer of 1914, their troops were supposed to be home by Christmas.
"It will be a very short war - a month, six weeks, perhaps," a French lieutenant, Charles Delvert, recalls a comrade telling him at the outset of the conflict.
"'No', I told him, 'It will be a drawn-out war - at least three months,'" he writes in his diary.
French and German generals alike forecast lightning offensives lasting just a few weeks in the plains of north and eastern France where most of the fighting eventually took place.
But by the time the first major battle drew to an end on the Marne river in September, such optimism lay buried along with the half million men already dead or wounded, at the outset of the four cataclysmic years of World War I.
The Schlieffen Plan was a German war strategy that aimed to crush French forces before British reinforcements could arrive, and before Russia could mobilise its population and pose a threat to Germany's east.
Within six weeks, German troops and heavy artillery were to have marched through the Netherlands and Belgium to the French border, with politicians in Berlin standing behind their military chiefs.
French generals had devised their own war strategy, the Plan XVII, based on lessons from their 1870 loss of Alsace and Lorraine to Germany, and General Joseph Joffre had the support of President Raymond Poincare.
Joffre believed that motivated infantrymen would cut German forces in two with a drive through the two disputed regions.
Young French farmers, who made up two fifths of conscripted troops, were called up from their fields to head for the front.
Many believed they would be back in time for the grape harvest in late September, while the pessimists among them allowed that victory might take a few months more, says historian Jean-Jacques Becker.
So certain were they of a short war that both the French and German sides had planned for limited ammunition - and were to run into severe shortages from September.
Quickly, both the French and German plans came undone.
Within weeks, French soldiers were pushed back - though they made a orderly retreat, and requisitioned Paris taxis to get fresh troops to the front.
Germans forces advanced to within 50 kilometres (30 miles) of the capital, forcing the government to flee south to Bordeaux, before they were stopped on September 6-9 in the first Battle of the Marne.
Neither the Battle of the Marne nor the First Battle of Ypres in October delivered a conclusive outcome despite horrific casualties.
By early 1915 the German and Allied forces were left facing off in a virtual stalemate from the North Sea to Switzerland.
And instead of Christmas at home, French and German troops spent it digging dismal trenches to shield themselves from artillery fire, on what became known as the Western Front.