Gas attack at Hulluch The Gas Attack at Hulluch was an engagement in World War I from 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 . 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 . Prelude . German offensive preparations . The German began preparing for the attack during April and placed about cylinders along a front from Cité St . Elie to Loos , where no man ' s land had been only apart since the Battle of Loos ( October 1915 ) . German artillery began a systematic bombardment of British observation posts , supply points and communication trenches , supplemented by trench mortars and rifle grenades . Shelling diminished from and on 26 April the positions of the British 16th Division were bombarded and the 12th Division front was raided . The next day was fine and warm , with a wind blowing towards the British lines . British defensive preparations . A German soldier deserted on the night of and warned the British that an attack on the Hulluch front , probably with gas , was imminent , which confirmed indications already noticed by the British . Rats had been seen moving away from the German trenches , which was inferred to be due to leaky gas cylinders . The systematic bombardment of British defensive positions and the testimony of the deserter led Lieutenant - General C . T . McM . Kavanagh , the commander of I Corps , to warn the divisions : the 1st Division which held the line from Lens to Loos , the 16th Division in the centre from to Hulluch and the 12th Division to the north opposite The Quarries and the Hohenzollern Redoubt . The 15th Division relief of the 12th Division from was allowed to proceed . Four reserve artillery batteries were moved into the 15th Division area and all units were required to rehearse gas alerts daily . The British were equipped with PH helmets , which protected against phosgene up to a concentration of German plan . The 4th Bavarian Division was to follow - up a gas attack on 27 April with a ( minor operation ) of patrols against the British positions . Two days later despite less favourable winds , a second gas discharge was ordered and protests by the local commanders were overruled . Battle . German attacks . The German attack began on 27 April with the release of smoke , followed by a mixture of chlorine and phosgene gas later from on the fronts of Bavarian Infantry Regiment 5 and Bavarian Reserve Infantry Regiment 5 . The discharge on the front of Bavarian Infantry Regiment 9 was cancelled , as the direction of the wind risked enveloping the 3rd Bavarian Division on the right flank , in the Redoubt sector . At German artillery began a high - explosive , shrapnel and trench - mortar bombardment on the front of the 16th Division and the right flank of the 15th Division to the north , laid a barrage on communication trenches and fired lachrymatory shells into villages and British rear positions . At gas and smoke clouds rose from the German trenches and moved towards the British trenches , blown by a south - easterly wind . The gas cloud was so thick at the beginning that visibility was reduced to ; wearing gas helmets was necessary behind the front line and the smell was noticed away . Three German mines were exploded at another artillery bombardment was fired and a second gas cloud was discharged . Several raiding parties of about each followed the gas and three managed to get into the British trenches . One party entered the British front line at Chalk Pit Wood for about fifteen minutes , the second was quickly expelled from the lines north of Posen Alley , then caught by Lewis - gun fire in no man ' s land . The third party got into the trenches on the right flank of the 15th Division , just north of the Vermelles – Hulluch road and was promptly bombed out ; by the raiding parties had withdrawn . On 29 April the German infantry sent up a green then a red flare and at German artillery began to bombard the reserve and communication trenches of the 16th Division . A gas cloud was released , followed by white smoke from Chalk Pit Wood to Hulluch , after Bavarian Infantry Regiment 9 had been ordered to discharge the gas by higher authority , despite unfavourable winds . German raiding parties advanced as the gas moved very slowly and then veered about as it reached the British third line ; the German raiders were then engaged by British infantry with small - arms fire . The gas suddenly blew back towards the German lines and in the area of Bavarian Infantry Regiment 9 and Bavarian Infantry Regiment 5 , the troops of Pioneer Regiment 36 were not able to stop the discharge straight away and many troops were caught without gas masks on and lost about casualties . On the right flank the 3rd Bavarian Division recorded casualties . The German bombardment abruptly ended , as the gas dispersed southwards . British defence . At on 27 April a gas alert was raised in the 16th Division area and the divisional and corps artillery began a bombardment on the rear of the German lines , from whence the gas was being discharged . After thirty minutes , groups of German infantry about equipped with pistols and hand grenades , were seen heading for gaps in the British wire and repulsed by rifle and machine - gun fire . At about the Germans sprang three mines and fired another bombardment before sending another gas cloud , which caused many casualties to a Black Watch company , whose commander had ordered them to remove their gas helmets after the first gas cloud , under the impression that the helmets were useless after one exposure to gas . Behind the second gas cloud , larger parties of German infantry advanced and managed to get into the British trenches for brief periods at three points . At Chalk Pit Wood the British had a howitzer , which had been brought up in September 1915 to fire in support of an attack on Hulluch . Since the " Lone How " was only behind the British front line , orders had been given to destroy it , in the event of a German raid and a demolition charge had been left on the gun with a lit fuze . The 48th Brigade recaptured the wood and a few hours later the gun was discovered intact , the fuze having gone out . The howitzer was so well camouflaged that the German radiers had not noticed it . British artillery - fire was believed to have destroyed some German gas cylinders , when German troops were seen to climb out of their front trenches and run to the rear , amid British small - arms fire . Eighty dead German soldiers were counted later in and around the British front trenches . By the German raid was over and during the night two British battalions were relieved ; the rest of 28 April was quiet except for a raid by the 1st Division , at the " Double Crassier " near Loos . On 29 April at a German artillery bombardment and gas discharge began on the 16th Division front but the expected attack did not occur . German troops were seen massing in the trenches near Hulluch at and small numbers advanced towards the British trenches , where they were engaged by small - arms fire . The German gas then reversed course and German infantry on a front of ran to the rear , through the gas and British artillery - fire , leaving about on the front of the 16th Division . Aftermath . Analysis . The 16th Division had a considerable number of gas casualties during the German attacks ; the greatest number of deaths occurred at the points on the British front where the gas was most concentrated . Anti - gas blankets fitted on dug - out entrances were found to be ineffective but Lewis - guns wrapped in blankets and sprayed with Vermorel during the passage of the gas cloud were only slightly affected . Some ammunition was made unusable and some rifles jammed , due to chemical deposits forming on the bolts . The troops most affected by the gas could not be relieved immediately but were exempted from carrying duties for the next day and no ill - effects were reported . British troops were said to have been greatly encouraged by the German fiasco but uneasy about the protection offered by their PH gas helmets . The troops were deceived by being told that the helmets issued to the 16th Division had not been properly impregnated with chemical neutralizers and that 16th Division gas discipline had been unsatisfactory . New " box respirators " , worn by Lewis gunners , were found to have worked well and production was expedited . Defensive artillery - fire had defeated most of the German infantry attacks and many German trench mortars were destroyed by the fire of 8 - inch and 9 . 2 - inch howitzer s but relatively little artillery - fire was devoted to counter - battery bombardments . Casualties . On 27 April the 16th Division had lost and the 15th Division reported Total British casualties were whom gas casualties , killed . German casualties in Bavarian Infantry Regiment 5 , Bavarian Reserve Infantry Regiment 5 , Pioneer Regiment 36 who operated the gas cylinders and other non - infantry troops were not known in 1932 , when the British Official History was published . Bavarian Infantry Regiment 9 had gas , of whom and there were gas casualties in the 3rd Bavarian Division , of whom four men died . A contemporary French intelligence summmary recorded in the 4th Bavarian Division from 27 – 29 April and during October 1918 , an officer of the British 15th Division found the graves of gas casualties from the gas discharges , at the cemetery at Pont - à - Vendin . In 1934 Foulkes wrote that a diary taken from a captured soldier of the 4th Bavarian Division , recorded casualties in the division and in 2002 Hook and Jones recorded from the German gas which blew back on 29 April .