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Renault, File, Associated Press
In this Sept. 7, 1914 file photo provided by French car manufacturer Renault, a Renault Type AG1, known as Taxis de la Marne, line up in France. The Renault Taxi de la Marne (Marne Taxi) is an automobile manufactured between 1905 and 1910 by Renault and was used as a taxicab. The name Taxi de la Marne was not used until the outbreak of World War I, when the fleet of Paris taxis was requisitioned by the French Army to transport troops from Paris to the First Battle of the Marne in early September 1914.

PARIS — The next time you flag a taxi on a crowded city street, spare a thought for the cabbie — and perhaps consider a bigger tip.

Weeks after World War I erupted, with the capital under threat from German invaders, French military chiefs devised a novel way for soldiers to travel to the front lines: by taxi.

To that end, they requisitioned hundreds of cabs, and their drivers were charged with the risky mission of getting thousands of troops to the battlefield.

This weekend, France honors the centennial of the "Taxis of the Marne," which have become the stuff of legend for millions of French school kids present and past. Paris City Hall, the Defense Ministry and private company Alpha taxis plan commemoration parades on Sunday that will include 10 taxis from the era.

Germany opened the Western Front on Aug. 4, sweeping into Belgium and hoping to overwhelm France before Russia had a chance to fully mobilize to the east. The lightning-fast Schlieffen plan aimed to bring German forces into Paris within weeks. After the guns of August blared, the French army looked as if it was on way to defeat.

On Sept. 6, 1914, Kaiser Wilhelm's troops were just a few dozen kilometers northeast of Paris. The French army requisitioned the taxis over two days to carry bedraggled troops returning from the collapsed front back to new battle lines. The call-up was part of a rising, nationwide war effort that also commandeered horses and called up more than three French million peasants to drop plowshares for guns.

Gen. Joseph Gallieni, the military governor of Paris who concocted the plan, ordered the taxis to gather on a grassy esplanade in front of the gold-domed Invalides military museum, which honors war victims and is the burial site of Napoleon Bonaparte. The commute to battle through the Paris environs must have been quite a sight: A rumbling caravan of hand-cranked red cars with bright yellow spokes packed a half-dozen soldiers behind primly-dressed drivers.

In that day, a motorcade was as much a technological innovation as unmanned drones might be considered in conflicts today.

For a bloody four-year war in which millions on both sides were mobilized, a few thousand troops didn't matter much at first sight. But the psychological impact on a nation used to "Belle Epoque" Paris comforts was critical. The French were beginning to seriously heed President Raymond Poincare's call for a "sacred union" of civilians and soldiers in the war effort.

"Taxi drivers were generally from modest backgrounds, so they represented the soul of Paris to some extent," said Laurent Lasne, author of a French book published last month on the taxis. As for the soldiers, he said, "they were tired ... The taxis were a rather nice surprise."

Time was of the essence. Train services were overloaded or unavailable. In came the taxis, mainly red Renault AG1s. They clocked an average 25 kilometers per hour (15 mph), according to the Web site of the national museums authority.

Paris was in a siege mentality, with shops and restaurants facing a 9 p.m. curfew to close their doors. Checkpoints cropped up on the city's edges. The U.S. ambassador predicted the city would fall in 48 hours.

"Everybody thought that Paris was finished. Everybody thought that the Germans, if they had followed the roads straight, would run right into Paris," said Lasne. "Instead of heading straight to Paris, the Germans started moving to the east."

According to the French Senate's Web site, the soldiers crammed five to a vehicle in a caravan of about 1,100 taxis, amounting to "the first time that the automobile was used for military ends." That's a slight exaggeration: Lasne said only about 700 cabs were actually involved. Historians seem to agree that a total of about 5,000 soldiers took part.

Lasne also debunked some illustrations showing troops and taxis cheered in a thankful Paris. In fact, the vehicles were empty but for their drivers, until they reached the suburbs of Livry-Gargan and Gagny.

Once there, crowds did turn out. Mothers, sisters and spouses poured out into the streets of the towns along the route, cheering them on with dry sausage, bread and wine.

With British expeditionary troops at their side, the French scored their first victory of the war at Marne in September 1914, providing a moment of French euphoria and setting the stage for four years of devastating trench warfare.

Gallieni, who died before the four-year conflict ended, played up the courage and national fervor of the drivers.

"Once they understood the importance of the task they had to cooperate in, the taxi drivers displayed totally remarkable fervor," he wrote in his memoirs. "They felt proud of the service asked of them, and when I asked one if he wasn't afraid of the mortars, he responded: 'we'll do like our comrades, we'll go where we have to.'"

They nevertheless got paid, even if the penny-pinching War Ministry doled out less than one-third of the paycheck at the time. The rest was paid after the war was over.

Raf Casert contributed from Brussels.