Édouard de Castelnau was a French general of the First World War, partly responsible for the aggressive French strategy at the start of the war. He was born into an aristocratic family (his full name was Noel Joseph Édouard de Curières de Castelnau) that had provided generals for both Napoleon I and Napoleon III, and was a staunch Roman Catholic. In secular egalitarian France this made him unpopular with many politicians, and after the war meant that he could not be made a Marshal of France.
Castelnau graduated from St. Cyr in 1870, and was immediately involved in the Franco-Prussian War. Over the next forty years he steadily rose through the ranks, gaining experience as both a staff and line officer, and become known as the French Army’s expert of staff work. His politics cost him his place on the General Staff in 1900, when he was removed for expressing anti-Dreyfusard opinions. After leaving the General Staff, he took command of an infantry regiment at Nancy, where he would late see much fighting.
In 1911 he was appointed as the first deputy chief of staff, under General Joffre, who had little knowledge of staff work. In this position he played a key part in the development of Plan XVII, the French war plan in place at the outbreak of the First World War. The main French offensive at the start of the war would be launched into Alsace-Lorraine, two provinces lost to German after the Franco-Prussian War. Castelnau was one of many French planners who did not believe that the Germans would have enough men to launch an offensive through Belgium and also defend their own border with France.
At the start of the First World War Castelnau had command of the Second Army, based at Nancy. As the war plan demanded, but despite Castelnau’s own doubts, this army began its offensive, towards the German fortress of Morhange (battle of Lorraine 14 August-7 September 1914). As the advance continued Castelnau came under pressure to move in two different directions – south to keep touch with the First Army, north to prevent the Germans interfering with the movements of the French Third and Fourth Armies further north (battle of the Ardennes, 20-25 August 1914).
The Germans slowly withdrew in front of the French armies until 20 August, when they launched their counterattack. After a day of fighting that saw one of Castelnau’s sons killed at Morhange, Castlenau was forced to order his army to retreat back to Nancy and the line of the River Meurthe. Depressed by the loss of his son and the failure of the offensive, he was even willing to retreat back to the Meuse and abandon Nancy to the Germans if that was what it would take to regain touch with Dubail to the south. General Foch, at that time commander of Castlenau’s XX corps, was able to convince him to make a stand at Nancy, and in the resulting fighting repeated German attacks were held off (battle of the Grande Couronne of Nancy, 25 August-11 September 1914).
At the fighting died down in Lorraine, the focus of the war moved north, where the Germans made their main attack. While Castelnau was fighting around Nancy, the first Battle of the Marne (5-10 September 1914) turned back the main German offensive. The Allied counterattack was halted at the Aisne (first battle of the Aisne, 13-28 September 1914), and both sides turned north, hoping to find an open flank (Race to the Sea).
In mid-September the Second Army at Nancy was dissolved, and a new Second Army formed to the south of Amiens, still commanded by Castelnau. His army was reinforced with four territorial divisions, and Castelnau was given orders to advance around the German right flank. This advance began on 22 August, against limited opposition, but the Germans was also moved troops to the area and on 24 August fighting raged from Albert, just north of the Somme, down to Noyon (first battle of Picardy, 22-26 September 1914).
The focus of the fighting then moved further north, first to Albert (battle of Albert, 25-29 September 1914) and then to Arras (first battle of Artois, 27 September-10 October 1914). Castelnau remained in overall command of this entire front until 4 October, when a new Tenth Army was created at Arras. The Race to the Sea ended in failure for both sides – neither side was able to find an open flank, and the Western Front now stretched from Switzerland to the Channel.
In June 1915 Castelnau was promoted to command the Centre Group of Armies, with General Pétain as one of his army commanders. The two men clashed over the best way to launch attacks – Castelnau still believed in the power of the infantry offensive, while Pétain was convinced that no attack could succeed without a massive artillery bombardment. The main action during his time in charge of the Centre Group was the second battle of Champagne (25 September-6 November 1915). The French captured the German front line, but their second line was still intact, and the battle bogged down. The French advanced at most two and a half miles, without ever capturing the German second line, at a cost 143,567 casualties.
At the end of 1915 Castelnau returned to staff work, as Joffre’s chief of staff. His first mission was a trip to Salonika, to regain central control over the activities of Generl Sarrail. In January 1916 he main an inspection of the defences of Verdun and was alarmed at what he saw, ordering the construction of a new line of defences on the eastern bank of the Meuse. This was too late, for on 21 February 1916 the Germans launched their great offensive at Verdun. Castlenau was rushed back to the city (25 February) with plenipotentiary authority. Once there he decided that the city must be held, and played a part in getting General Pétain appointed to command the defence.
At the end of 1916 Joffre was removed as commander-in-chief. Castelnau was considered as a possible replacement, but he had been too close to Joffre, and the post was given to General Nivelle. Castelnau was dispatched to Russia, then on the verge of revolution. Nivelle’s tenure of the top post was short, and after he was replaced by General Pétain. Castelnau was appointed to command the Eastern Group of Armies. At the end of the war he was planning another invasion of Lorraine, part of the unneeded 1919 campaign.
After the war Castelnau served in the Chamber of Deputies from 1919-1924. Despite surviving until 1944, Castelnau did not write memoirs, so his image was shaped by the hostile views of Joffre and Foch. Joffre believed him to be defeatist, and partly to blame for the failure to turn the German right flank after the first battle of the Aisne, but this fails to take into account the German movements into the same area.