Editing Maxime Weygand (section)

==== Early war ====
At the outbreak of the war, he was posted as a staff officer with the [[5th Hussar Regiment|5ème Hussars]]. His regiment was deployed to the Franco-German border on 28 July 1914 and later fought at the [[Battle of Morhange]]. On 17 August, he became chief of staff to [[Ferdinand Foch]], the commander of the new [[9th Army (France)|Ninth Army]].{{sfn|Clayton|2015|p=13, noting deployment in 28 July, war with Germany on 3 August, and promotion to Foch's staff on 17 August}} Weygand served under Foch for much of the rest of the war.

The professional partnership between Foch and Weygand was close and fruitful, with Weygand operating as a highly competent subordinate able to translate Foch's instructions into clearer orders, analyse ideas, and collate information. Foch referred to Weygand with praise, believing that their views were practically identical.{{sfn|Clayton|2015|pp=17–18, noting Foch's remark: "Ask Weygand, it is the same"}} Weygand finalised the plans for the 9th Army's attack at the [[First Battle of the Marne]] and, in doing so, became one of the first staff officers to reconnoitre the battlefield from the air.{{sfn|Clayton|2015|p=21. "At one point he flew with one of France's earliest military avaiators, [[Marcel Brindejonc des Moulinais|Marcel-Georges Brindejonc des Moulinais]], to make a personal reconnaissance of the battlefield, at the time a novel achievement for a senior staff officer"}} Weygand supported Foch, who was appointed to coordinate the Belgian, British, and French forces in the northern sector, during the [[Race to the Sea]] and [[First Battle of Ypres|First Ypres]].{{sfn|Clayton|2015|p=21}} Weygand was promoted to full colonel in early 1915.{{sfn|Clayton|2015|p=21}}

The mounting French casualties over the course of 1915 were reflected in Weygand's campaign notes; the need for further cooperation between French and British armies utilised Weygand's communicative skills and he developed a working relationship with some British counterparts.{{sfn|Clayton|2015|p=26, noting as exception [[Edward Spears]]}} Weygand was promoted to [[Brigadier General#France|général de brigade]] in 1916. He later wrote of the [[Battle of the Somme|Anglo-French Somme Offensive in 1916]], at which Foch commanded French Army Group North, that it had seen "constant mix-ups with an ally [the British] learning how to run a large operation and whose doctrines and methods were not yet in accordance with ours".{{sfn|Greenhalgh|2005|p=70}} At a meeting on 3 July 1916 where Joffre and Haig came to non-speaking terms, Weygand, Foch, and [[Sir Henry Wilson, 1st Baronet|Henry Wilson]] were able to restore a working relationship between the armies. He also took effective command of the army group as alternate when Foch was in ill health; during tensions between Foch and subordinates, Weygand helped to mediate disputes.{{sfn|Clayton|2015|pp=27–28}}

After Joffre was replaced by [[Robert Nivelle]] in late 1916, criticism of Foch also intensified, leading to Foch being relieved of his northern command; Weygand saw the politician's treatment of Foch as intolerable. At Foch's suggestion, Weygand's name was submitted for command of an infantry brigade, but after Foch was assigned out of inactivity to instead create a contingency plan for a German invasion of France via Switzerland, Weygand decided to stay with Foch.{{sfn|Clayton|2015|pp=28–30}} As part of this planning, Weygand served as head of a mission to Switzerland to discuss Anglo-French support if Switzerland were breached by German troops.{{sfn|Clayton|2015|p=30}} Weygand later accompanied the British [[Chief of the Imperial General Staff]], General [[Sir William Robertson, 1st Baronet|Sir William Robertson]], on an inspection of the [[Italian front (World War I)|Italian front]] in early 1917 to discuss Anglo-French support for Italy's [[Battles of the Isonzo|Isonzo campaign]]. When Weygand and Foch were briefed on the [[Nivelle offensive]], the two men expressed misgivings.{{sfn|Clayton|2015|p=31}} After its failure, Nivelle was removed as French commander-in-chief and replaced with [[Philippe Petain]]. Foch was appointed chief of the army general staff in 19 May 1917; writing to his wife, Weygand expressed his loyalty to Foch and gave up his applications for a field command.{{sfn|Clayton|2015|p=32}}