The World War I First Battle of the Marne featured the first use of radio intercepts and automotive transport of troops in wartime.
After French commander in chief Joseph Joffre ordered an offensive in September 1914, General Michel-Joseph Maunoury's French Sixth Army opened a gap between Germany's First and Second Armies. Maunoury exploited the gap with help from the French Fifth Army and British Expeditionary Force, while Ferdinand Foch's Ninth Army thwarted the advances of the German Second and Third Armies. By Sept. 10, the Germans embarked on a retreat that ended north of the Aisne River, beginning a phase of the war that would be marked by trench warfare.
The First Battle of the Marne was fought to the north and east of Paris in early September 1914. The opportunity opened for Anglo-French forces to reverse the hitherto victorious German advance through Belgium and France when First Army commander Heinrich von Kluck, who anchored the right wing of the German advance, swung north, rather than west, of Paris, across the front of Michel-Joseph Maunoury's French Sixth Army.
Alerted by French air reconnaissance and radio intercepts, the first time either had been used in a major conflict, French commander in chief Joseph Joffre ordered an attack. On September 6, Maunoury, reinforced by troops, rushed to the front in requisitioned Paris taxis and buses—the first extensive use of motorized transport in wartime and forever celebrated as the "taxis of the Marne"—slammed into von Kluck's overextended army. Surprised, von Kluck recalled his advanced guard and swung his forces to the southwest to meet Maunoury's attack. But in doing so, von Kluck lost contact with Karl von Bulow's Second Army on his left flank.
The British Expeditionary Force (BEF) rallied together with elements of the French Fifth Army to surge into the breach von Kluck had opened in the German front. The tenacious defense of Ferdinand Foch's Ninth Army in the St.-Gond marshes against repeated attacks of the German Second and Third Armies frustrated German attempts to dislocate the French thrust by collapsing Joffre's right wing. On September 10, German chief of staff Helmuth von Moltke the younger ordered his forces to regroup on a front between Soissons and Verdun. Joffre pursued into September 13, when French attacks failed to dislodge German positions north of the Aisne. Each army then began a series of flanking maneuvers known as the "race to the sea," which left in its wake a system of linked trenches protected by barbed wire.