The 101st went to war on mobilisation on 2nd August. The regiment's three battalions were made up to their full strength with the younger and fitter, reservists, and it concentrated at its Saint-Cloud depot. After leaving the Army at the end of his conscription period, every man was given a booklet (the fascicule de mobilisation) that, amongst other things, specified on which day he was to report to his depot after general mobilisation was declared. The mobilisation notices tabulated these dates leaving no-one in any doubts as to when they should report. The older reservists formed a reserve regiment, the 301st Infantry (which served with VI Corps in Third Army). The oldest were directed into the 29th Territorials, which formed part of the Paris garrison.
The 101st formed part of 7th Division, part of IV Corps (Fourth Army). The corps concentration area was designated as Verdun, and the regiment proceeded there by railway, via Reims, Sainte-Menehould, Clermont-en-Argonne and Dugny, arriving there on the 8th. The regiment then marched to its billets in and around the villages to the north-west of the city: the 1st Battalion at Brabant-sur-Meuse (twenty-eight kilometres, that Delvert found 'very tough'), the 2nd Battalion and the regimental HQ at Samogneux, and the 3rd Battalion at Haumont-près-Samogneux.
The colonel of the 101st in 1914 was Léon Gaston Jean-Baptiste Farret (1861-1928). He was a hugely experienced officer, much of it spent in the colonies - summed up by Delvert as 'short, fat, pince-nez, a former colonial'. He was commissioned into 1st Zouaves in 1881; as a lieutenant, he subsequently served with 136th Infantry, 1st Zouaves, both Annamite and Tonkinois tirailleurs, and 141st Infantry. Promoted to captain, he served with 162nd and 45th Infantry before going to 1st Etranger. He served with both the 1st and 2nd Regiments of the Foreign Legion, before getting his majority (CO of a battalion) in 1900, serving first with 3rd Zouaves, then back to 1st Etranger. He took command of the 101st in 1913. After less than four weeks at war, he took command of his brigade, which he continued to lead until February 1917. Following the reorganisation of each infantry division and the abolition of brigade-level commands, he was made infantry commander of 7th Division, then in April 1918, of 165th Division. That was his last front-line command; after the war, he was given 11th Colonial Division (1918-19) serving with the occupation forces in the disputed Banat region of the former Austria-Hungary, then after a spell of leave, of 27th Division (1919-23). He then retired from active service. His Légion d'Honneur file is here.
The regiment's second-in-command was Lieutenant Colonel François Marc Celestin Ferran (1865-1914). He was a thorough infantryman, graduating from Saint-Cyr in 1883. He served with the 12th Infantry, 24th Chasseurs, 9th, 40th and 118th Infantry, 6th Chasseurs, 134th, 59th and 25th Infantry Regiments, as well spending time on the staff of XV Corps, and as assistant lecturer in applied tactics at the staff college, the Ecole Supérieure de Guerre. Delvert describes him as 'tall ... angular features, small ... moustache'. His Légion d'Honneur file is here; his MPLF card is here.
After spending 9th August in place, the regiment headed north, in the direction of Mangiennes and the Belgian frontier. The next few days were spent in and around Mangiennes and Pillon. Gunfire was heard in the distance, and on the 15th some shots were exchanged between patrols of the regiment's 3rd Battalion, supported by a troop of 14th Hussars and three batteries of 26th Artillery, and German patrols.
On 21st August, the regiment was on the move again, to the north-east, towards the Belgian town of Virton.
Photos: the mobilisation poster from Wikipedia; Colonel Farret (shown in October 1916 outside his HQ in Redoubt MF4 (near the Ouvrage de Froideterre) at Verdun, from Collections BDIC; Lt. Colonel Ferran from a genealogy site here.