PARIS — The echoes of the guns of August 1914 had barely subsided when France faced its first crisis of World War I. By early September, the German army had moved through Belgium and was within 30 miles of Paris; the French government was preparing to decamp to Bordeaux, and panic spread through the city.

The French were back on their heels. Gen. Joseph Joffre organized a counterattack, and by Sept. 6 his troops were fighting the Germans along the Marne River. With the outcome — and possibly the fate of France — in the balance, General Joffre called for reinforcements from Paris.

Image Introduced in 1917, the Renault FT Char Léger, or light tank, has a rotating turret and a rear engine, with the driver sitting in front. It is considered the first modern tank. Credit... Peter Sigal/The New York Times

But the railways were clogged and no trucks were available, so the military commander of Paris, Gen. Joseph Gallieni, hailed the city’s taxi drivers. On the evening of Sept. 6, hundreds of cabs assembled at Les Invalides, the military hospital, and by morning a convoy of impossibly top-heavy Renault AG1s with tiny 1.2-liter 2-cylinder engines was puttering toward the front.