The Gas Attack at Hulluch was an engagement in World War I from 27–29 April 1916, between divisions of the II Bavarian Corps and divisions of the British I Corps. Just before dawn on 27 April the 16th Division and part of the 15th Division were subjected to a German cloud gas attack, near the German-held village of Hulluch, a mile north of Loos.

Date 27–29 April 1916 Location Hulluch, France Result British success
Belligerents
United Kingdom	Germany  Bavaria
Commanders and leaders
Charles Kavanagh William Bernard Hickie	O. von Stetten
Strength
I Corps (12th, 15th and 16th divisions)	II Royal Bavarian Corps (3rd and 4th Bavarian divisions)
Casualties and losses
1,980 (1,260 gas casualties, 338 killed)	(incomplete) c. 1,500 (1,500 gas casualties)

The gas cloud and artillery bombardment were followed by raiding parties, which made temporary lodgements in the British lines. Two days later another gas attack was launched, which blew back over the German lines and caused a large number of German casualties, which were increased by British troops firing at German soldiers as they fled in the open. The German gas was a mixture of chlorine and Phosgene, which was of sufficient concentration to penetrate the British PH gas helmets. The 16th Division was unjustly blamed for poor gas discipline and it was put out that the gas helmets of the division were of inferior manufacture, to allay doubts as to the effectiveness of the helmet. Production of the Small Box Respirator, which had worked well during the attack, was accelerated.