Huế chemical attacks The Huế chemical attacks occurred on 3 June 1963 , when soldiers of the Army of the Republic of Vietnam ( ARVN ) poured liquid chemicals from tear gas grenades onto the heads of praying Buddhist s in Huế , South Vietnam . The Buddhists were protesting against religious discrimination by the regime of the Roman Catholic President Ngô Đình Diệm . The attacks caused 67 people to be hospitalised for blistering of the skin and respiratory ailments . The protests were part of the Buddhist crisis , during which the Buddhist majority in South Vietnam campaigned for religious equality after nine people were killed by government forces while defying a ban that prevented them from flying the Buddhist flag on Vesak . The incident prompted the United States to privately threaten to withdraw support for Diệm ' s government and when the Americans finally reduced aid a few months later , the army took it as a green light for a coup . An inquiry determined that the chemical used in the attack was a liquid component from old French tear gas grenades that had never functioned properly . The findings exonerated the ARVN soldiers from charges that they had used poison or mustard gas . The outcry over the attack had already forced Diệm to appoint a panel of three cabinet ministers to meet with Buddhist leaders for negotiations regarding religious equality . The talks led to the signing of the Joint Communique , but the policy changes it provided were not implemented and widespread protests continued , leading to the assassination of Diệm in a military coup . Background . In a country where demographic surveys estimated the Buddhist majority to be between 70 and 90 percent , President Ngô Đình Diệm ' s policies generated claims of religious bias . A member of the Roman Catholic minority in Vietnam , he pursued pro - Catholic policies that antagonized many Buddhists . Specifically , historians regard the government as being biased towards Catholics in public service and military promotions , as well as in the allocation of land , business favors , and tax concessions . Diệm ' s family also seized businesses belonging to Buddhists in order to enrich themselves . Many officers in the Army of the Republic of Vietnam converted to Catholicism in the belief that their military prospects depended on it . Forgetting that he was talking to a Buddhist , Diệm once told a high - ranking officer , " Put your Catholic officers in sensitive places . They can be trusted . " The distribution of firearms to village self - defense militias intended to repel Vietcong guerrillas resulted in weapons only being given to Catholics . Some Catholic priests ran their own private armies , and in some areas , forced conversions , looting , shelling and demolition of Buddhist pagoda s occurred . Some Buddhist villages converted " en masse " to receive aid or avoid being forcibly resettled by Diệm ' s regime . The Catholic Church was the largest landowner in the country , and the " private " status that was imposed on Buddhism by the French colonial authorities , which required official permission to conduct public Buddhist activities and restricted the construction of Buddhist temples , was not repealed by Diệm . Furthermore , the land owned by the Catholic Church was exempt from redistribution under land reform programs . Catholics were " de facto " exempt from the corvée labor that the government obliged all citizens to perform and the government disproportionately allocated funding to Catholic majority villages . Under Diệm , the Roman Catholic Church enjoyed special exemptions in property acquisition , and in 1959 , he dedicated the country to the Virgin Mary . The Vatican flag was regularly flown at major public events in South Vietnam . On 7 May 1963 , government officials invoked a rarely enforced 1958 law known as Decree Number 10 to prohibit the display of religious flags , forbidding Buddhists from flying their flag on Vesak , the birthday of Gautama Buddha . The application of the law caused indignation among Buddhists in the lead - up to the most important religious festival of the year , as Catholics had been allowed to display Vatican flags a week earlier at a celebration for Diệm ' s elder brother , Archbishop Ngô Đình Thục . On 8 May , in Huế , a crowd of Buddhists protested against the ban on the Buddhist flag . The police and army broke up the protest by opening fire and throwing grenades at the demonstrators , leaving nine dead . Diệm ' s denial of governmental responsibility for the incident , and instead blaming members of the Vietcong insurgency , led to growing discontent among the Buddhist majority . The incident spurred a protest movement by Buddhists against the religious discrimination of Diệm ' s Roman Catholic - dominated regime . The dispute came to be known as the Buddhist crisis , and it provoked widespread and large - scale civil disobedience throughout South Vietnam , persisting throughout May . The objective of the protests was to have Decree Number 10 repealed , and to force the implementation of religious equality . At the time , the United States , the main backer of South Vietnam in the Cold War , had 16 , 000 military advisers in the country to assist the Army of the Republic of Vietnam in the war against the Vietcong insurgency , which sought to reunify Vietnam under communist rule . Washington wanted the dispute with the Buddhists to be resolved quickly so that it would not dampen public morale and detract from the fight against the Vietcong . Incident . On 3 June , Buddhists held another series of protests across the country . In the morning , attention focused on the capital Saigon , where approximately 500 Buddhist laypeople , mostly youths , protested in front of the Government Delegate ' s office while 300 troops stood by . The crowd and a government official equipped with a loudspeaker exchanged taunts and accusations . When the official claimed that Vietcong were among the crowd and attempting to cause trouble , the troops aimed their firearms at the protestors . When the crowd responded by taunting the soldiers as " stupid killers " , the troops fixed bayonets to their guns and put on gas masks before charging at the protestors and throwing tear gas grenades at them . Some of the demonstrators ran away , while others remained stationary and began praying . Deaths and injuries were averted when a Buddhist leader urged the protestors to either retreat to a pagoda and receive medical treatment for the tear gas or to go home . When the entrance to the pagoda was blocked with barbed wire , some protestors simply sat on the ground and continued praying . After a standoff lasting almost three hours , troops wearing gas masks forcibly dispersed the crowd . The situation was worse in Huế , where Diệm had banned demonstrations and ordered his forces to arrest those who engaged in civil disobedience . At 13 : 00 , some 1 , 500 protestors attempted to march towards the Từ Đàm Pagoda in Huế for a rally , having gathered at the Bến Ngư Bridge near the Perfume River . A confrontation ensued when the protestors attempted to cross the bridge . Six waves of ARVN tear gas and attack dogs failed to disperse the crowd . Government officials stood on trucks , using loudspeakers to call out above the noise , urging the Buddhists — primarily high school and university students who had arrived on bicycles — to disperse . The announcements were met by jeers when the government spokesperson blamed the unrest on the Vietcong . At 18 : 30 , the military personnel at the scene dispersed the crowd by emptying vials of brownish - red liquid on the heads of praying protestors , resulting in 67 Buddhists being hospitalized for chemical injuries . The symptoms consisted of severe blistering of the skin and respiratory ailments . The crowd responded angrily to the apparent use of poison gas , and the incident became a public relations disaster for Diệm . Reaction and investigation . By midnight , tensions were high as a curfew and martial law were enacted . Rumors circulated that three people had died , and " Newsweek " reported that police had lobbed blister gas into the crowd . Reports citing reliable sources claimed that Diệm was planning a military showdown against the Buddhists . US consul John Helble suspected that the ARVN troops had used tear gas , and in a report to the US Embassy , Saigon , he noted that " possibly another type of gas which caused skin blisters " was used . Helble reported that the substance , although unidentified , had raised concerns by the US State Department that poison gas was used because the symptoms were not consistent with standard tear gas . If this were the case , Helble concluded that the United States should tell Diệm that his regime must condemn the actions of the troops and punish the culprits . If Diệm refused , the United States should threaten to publicly condemn and distance itself from Saigon . With the US also decrying the use of troops against civilian protests , the South Vietnamese government complained that unlike their Saigon counterparts , the Huế police were not trained in riot control . Diệm ' s authorities requested that the Americans airlift 350 military personnel from Vũng Tàu in the far south to quell the protests in Huế , but the Americans refused . William Trueheart , who was in charge of the US Embassy , Saigon while Ambassador Frederick Nolting was on holiday , confronted Secretary of State Nguyễn Đình Thuận about the allegations of blister gas usage the next day . Thuận appeared to be astounded and asked Trueheart what blister gas was . Trueheart explained that the symptoms of the victims were consistent with those of mustard gas and passed on the US threat to denounce the regime for the chemical attacks . Thuan started an inquiry into the usage of chemical weapons on the protestors . The investigation exonerated the Diệm regime of the most serious allegations of using poison or mustard gas . Before the president was deposed in November , the inquiry ' s report declared that only tear gas was used , and that the liquid components of the grenades were poured onto the protestors after they had failed to vaporize as they were designed to . A further commission chaired by General Trần Văn Đôn prior to February 1964 concluded that the tear gas was left behind by French colonial forces in the 1950s . The tear gas used came in glass containers in the form of a liquid that was transformed into gaseous vapor upon activation by acid . The injuries were attributed to the acid failing to activate the liquid into gaseous form . United States Army chemists in Maryland confirmed that the tear gas had come from canisters dating back to French World War I stocks . During World War I , France had used tear gas containing a mixture of chloroacetone and ethyl bromoacetate against German troops at Ypres on the Western Front , which was known to strongly irritate mucous membrane s . Chloroacetone turns brown - orange when exposed to light , while ethyl bromoacetate is a yellow liquid at tropical outdoor temperatures . Both have similar colors to the liquid used on the demonstrators . Some varieties of French tear gas contained phosgene oxime or hydrogen cyanide . These two chemicals can be fatal , but none of the protestors in this incident died . Repercussions . Diệm responded to the controversy of the chemicals by agreeing to formal talks with the Buddhist leaders . He appointed a three - member Interministerial Committee , which comprised Vice President Nguyễn Ngọc Thơ as chairman , Thuan and Interior Minister Bui Van Luong . Despite continuing protests , including public self - immolation s by monks such as Thich Quang Duc , a Joint Communique resulting from the discussions was signed in mid - June , which promised to end the Buddhist crisis . The Joint Communique was not implemented and the situation continued to deteriorate , particularly after the Ngô family ordered South Vietnam ' s Special Forces to attack Buddhist pagodas across the country on 21 August . The U . S . condemned the raids , and began to cut aid to the Special Forces , which was effectively a private Ngô family army , in addition to other government programs that were closely identified with the ruling clan . Regarding such gestures as a green light , and safe in the knowledge that the US would not intervene in Diệm ' s defense , the army staged a successful coup in November , resulting in the assassination of the president . The removal of Diệm resulted in a period of political instability , as a series of military juntas deposed one another . This led to a deterioration in the military situation as the communist Vietcong made substantial gains against the ARVN , prompting the US to deploy hundreds of thousands of combat troops in 1965 , escalating the Vietnam War .