By 1916 the great buildup of the British army had produced a massive force designed to be thrown into action side by side with the forces of France. A potent force pushing for such a British effort was the growing feeling in France that its army was bearing the brunt of the fighting and losses on the western front. Indeed, total French casualties in 1915—killed, wounded, missing in action, and taken prisoner—reached the sickening figure of 1,549,000 men.i The joint offensive was scheduled to take place in spring around the Somme, but Germany struck first. The renewal of German offensive action on the western front did not aim at a breakthrough or a quick victory. In the view of General von Falkenhayn, Germany's best hope rested in a battle of exhaustion, forcing the French to fight under unfavorable circumstances in terms of terrain and supply, and inflicting intolerable losses on France's army. With France—what Falkenhayn called "Britain's arm on the continent"—crippled, the war could be brought to a negotiated conclusion favorable to Germany. The German offensive at Verdun, a historic fortress that no French government could lightly abandon, began in the snows of winter. The carnage started in February and lasted until the close of the year: its duration of ten months makes it the longest battle in history. German attacks hurt their own army almost as badly as they bled France's forces. Their assaults ran into tenacious French resistance. Advancing infantry found, as the Allies had in 1915, that artillery barrages left enough enemy machine guns intact to inflict intolerable casualties. Much of the fighting consisted of massive exchanges from heavy guns, and both sides inflicted comparable losses on one another. French leaders, notably General Philippe Petain, the army's leading specialist in defensive operations, kept their heads, and Petain maintained the army's stability by rotating units quickly in and out of Verdun. Located in an exposed salient and supplied by a single road, Verdun appeared to be impossible to supply. Petain found ways to bring in the needed supplies: improving the one available road (la voie sacree) and developing a massive and continuing flow of truck traffic. By the closing months of the year, Petain's successor at Verdun, General Robert Nivelle, took the offensive. After the prolonged slaughter, the battle lines were close to their starting point. Nearly 400,000 Frenchmen lost their lives in this hellish place; the Germans emerged almost equally ravaged, with 340,000 killed or missing.