The Battle of Loos was the largest British offensive mounted on the Western Front in 1915 during World War I. The first British use of poison gas occurred and the battle was the first mass engagement of New Army units. The British offensive was part of the attempt by the French to break through the German defences in Artois and Champagne and restore a war of movement. Despite improved methods, more ammunition and better equipment the Franco-British attacks were contained by the German armies, except for local losses of ground. Casualties in the Herbstschlacht (Autumn Battle) were high on both sides.

Date 25 September – 14 October 1915 Location Loos, France Result Stalemate
Belligerents
British Empire  India  United Kingdom	German Empire
Commanders and leaders
John French Douglas Haig	Rupprecht, Crown Prince of Bavaria Friedrich Bertram Sixt von Armin
Strength
6 divisions	3 divisions
Casualties and losses
59,247	c. 26,000

The battle was the British component of the combined Anglo-French offensive known as the Third Battle of Artois. Field Marshal Sir John French and Haig (GOC British First Army), both of whom initially regarded the ground, overlooked by German-held slag heaps and colliery towers, as unsuitable for an attack, persuaded themselves that the Loos attack could succeed, perhaps as the use of gas would allow a decisive victory.