The 45th Infantry Division, also known as the 45th Algerian Division, was an infantry division of the French Army that served in World War I. The 45th Division was formed on 19 August 1914 from personnel from Algeria, Morocco, and North Africa in general, within the 19th Military Region; The division consisted primarily of tirailleurs and Zouaves (both types of light infantry). The alleged first gas attack of the Western Front was launched against its positions (among other divisions) north of Ypres on 22 April 1915. Chemical weapons had already been used on the Eastern Front and there are some claims that use on the Western Front occurred prior to 22 April 1915. The division was disbanded on 27 March 1919 at Mainz.

Mobilized in the 19th region, from 19 August. 24 August – 6 September : transported by sea to Sète, then by rail to the south of Paris; where its journey temporarily halted. From 3 September, redeployed to the Le Mesnil-Amelot region.

6–13 September : engaged in the First Battle of the Marne. From 6 to 10 September, Battle of the Ourcq. Took part in the fighting towards Penchard, Chambry, Aisne, Barcy and Étrépilly, Seine-et-Marne. From 10 September, continued via Lizy-sur-Ourcq and Longpont (with the British Expeditionary Force), as far as Soissons. 13 September – 3 October : engaged in the first battle of the Aisne. Crossed the Aisne (river) towards Soissons and repeated fighting north of Crouy. Then stabilization of the front and occupation of a sector in this region. On 23 and 30 September, French attacks towards the Perrière farm and north of the Montagne Neuve farm.

3 October 1914 – 25 February 1915: withdrawal from the front and transport by railway to the Arras region. Engaged, from 5 October, in the First Battle of Artois. Fighting in the region of Bailleul-Sir-Berthoult, Roclincourt, Thélus and Écurie. Stabilization and occupation of a sector towards Roclincourt and La Targette (mine warfare). 31 October : front extended to the right towards the Maison Blanche. 5 November : Took part in the fighting towards Écurie and north. 16 November : reduced front on the left to the south of La Targette. 28 November : German attack towards Écurie; from 27 to 29 November French counter-attacks. 7–8 December : new German attacks and French counter-attacks. 17–18 February 1915 : French attacks.

25 February – 13 April : withdrawn from the front line to Avesnes-le-Comte; rest, then from 30 March sent to Doullens; refresher training. (Elements in sector with the 10th Army Corps (France), to Arras up to 2 March). From 6 April, transport by rail from the Doullens region to the south of Bergues. 13 April – 8 June : moved to the front line, to occupy of a sector towards Poelkapelle and Langemark (flanking the British Army). 22 April : German gas attack during the Second Battle of Ypres; French counter-attacks. Then occupied of a new sector towards Boezinge and Het-Sas. 16–17 May : French attacks on Hill 17 towards Pilkem. 20–21 May : German counter-attacks. 23 May : sector moved, right towards Wieltje and Boezinge. 30 May : new French attacks on Hill 17. 8 June – 30 September : relief by the British Second Army; bypass movement to the north, then occupied a new sector on the Yser, towards Boezinge and Steenstrate (flanking the British and Belgian armies). 30 September 1915 – 11 March 1916 : withdrew from the front line to the south-east of Bergues; rest and refresher training. From 21 November, elements in the Nieuwpoort sector.

11 March – 9 May : transported by rail in the Crépy-en-Valois region; rest. From 18 March, moved in stages to Jonchery-sur-Vesle; rest and work. From 20 April, transported by rail in the Sainte-Menehould region and rest in that of Triaucourt. 9–23 May : moved to the front line. Engaged in the Battle of Verdun between La Hayette and Avocourt Wood. Fighting in Camard wood. 23 May–9 June : withdrew from the front line to the west of Saint-Dizier; rest. From 30 May, transport by rail in the Châtel-sur-Moselle region; rest. 9 June – 9 August : moved to the front line, occupied a sector between Vezouze and Chapelotte. 9 August – 1 September : withdrawal from the front line to Rambervillers; rest. From 12 August, sent to the Saffais camp; refresher training. 25 August, transported by rail to the Grandvilliers region; rest.

1–16 September : transport by trucks to Fouilloy. Committed from 4 September in the Battle of the Somme, deployed towards the Hôpital farm and the Forest. On 13, 14 and 15 September, French attacks. 16 September – 6 October : withdrawal from the front line to Formerie; rest. From 29 September, transported by rail to the Dunkirk region; rest. 6 October 1916 – 12 January 1917 : moved to the front line, to occupy a sector between Nieuport and Saint-Georges.

12 January – 16 February : withdrawal from the front, transport by rail from Dunkirk to Chantilly; refresher training at the Pontarmé training camp and from 7 February, rest in Neuilly-en-Thelle. 16 February – 4 March : employed on working parties at Fitz-James, for the entrenched camp of Paris. 4 – 15 March : moved to the front line, to occupy a sector towards Beuvraignes and the Bois des Loges (excluded). 15 March – 2 April : withdrew from the front line to Montdidier, employed on working parties, then from 27 March transported by rail to Mailly-le-Camp; rest. 2 – 22 April : moved to the front line, via Mourmelon-le-Petit, then on the 5 April occupied the sector north of Prosnes. Engaged from 17 to 20 April in the Battle of the Hills (capture of Mount Haut and the Casque). 11 April – 19 May : withdrew from the front line, moved to Mourmelon-le-Grand; at rest in the vicinity of La Chaussée-sur-Marne.