the chief of staff of the army. for example, the emperor authorized the use of toxic gas on 375 separate occasions during the battle of wuhan from august to october 1938. they were also profusely used during the invasion of changde. those orders were transmitted either by prince kan'in kotohito or general hajime sugiyama. the imperial japanese army had used mustard gas and the us-developed (cws-1918) blister agent lewisite against chinese troops and guerrillas. experiments involving chemical weapons were conducted on live prisoners (unit 731 and unit 516). the japanese also carried chemical weapons as they swept through southeast asia towards australia. some of these items were captured and analyzed by the allies. historian geoff plunkett has recorded how australia covertly imported 1,000,000 chemical weapons from the united kingdom from 1942 onwards and stored them in many storage depots around the country, including three tunnels in the blue mountains to the west of sydney. they were to be used as a retaliatory measure if the japanese first used chemical weapons. buried chemical weapons have been recovered at marrangaroo and columboola. nazi germany the germans eventually used poison gas on survivors from the battle of kerch, may 1942. during the holocaust, a genocide perpetrated by nazi germany, millions of jews, slavs, homosexuals and other victims were gassed with carbon monoxide and hydrogen cyanide (including zyklon b). this remains the deadliest use of poison gas in history. nevertheless, the nazis did not extensively use chemical weapons in combat, at least not against the western allies, despite maintaining an active chemical weapons program in which the nazis used concentration camp prisoners as forced labor to secretly manufacture tabun, a nerve gas, and experimented upon concentration camp victims to test the effects of the gas. otto ambros of ig farben was a chief chemical-weapons expert for the nazis. the nazis' decision to avoid the use of chemical weapons on the battlefield has been variously attributed to a lack of technical ability in the german chemical weapons program and fears that the allies would retaliate with their own chemical weapons. it also has been speculated to have arisen from the personal experiences of adolf hitler as a soldier in the kaiser's army during world war i, where he was gassed by british troops in 1918. after the battle of stalingrad, joseph goebbels, robert ley, and martin bormann urged hitler to approve the use of tabun and other chemical weapons to slow the soviet advance. at a may 1943 meeting in the wolf's lair, however, hitler was told by ambros that germany had 45,000 tons of chemical gas stockpiled, but that the allies likely had far more. hitler responded by suddenly leaving the room and ordering production of tabun and sarin to be doubled, but "fearing some rogue officer would use them and spark allied retaliation, he ordered that no chemical weapons be transported to the russian front." after the allied invasion of italy, the germans rapidly moved to remove or destroy both german and italian chemical-weapon stockpiles, "for the same reason that hitler had ordered them pulled from the russian front—they feared that local commanders would use them and trigger allied chemical retaliation." stanley p. lovell, deputy director for research and development of the office of strategic services, reports in his book of spies and stratagems that the allies knew the germans had quantities of gas blau available for use in the defense of the atlantic wall. the use of nerve gas on the normandy beachhead would have seriously impeded the allies and possibly caused the invasion to fail altogether. he submitted the question "why was nerve gas not used in normandy?" to be asked of hermann göring during his interrogation after the war had ended. göring answered that the reason was that the wehrmacht was dependent upon horse-drawn transport to move supplies to their combat units, and had never been able to devise a gas mask horses could tolerate; the versions they developed would not pass enough pure air to allow the horses to pull a cart. thus, gas was of no use to the german army under most conditions. the nazis did use chemical weapons in combat on several occasions along the black sea, notably in sevastopol, where they used toxic smoke to force soviet resistance fighters out of caverns below the city, in violation of the 1925 geneva protocol. the nazis also used asphyxiating gas in the catacombs of odessa in november 1941, following their capture of the city, and in late may 1942 during the battle of the kerch peninsula in eastern crimea. victor israelyan, a soviet ambassador, reported that the latter incident was perpetrated by the wehrmacht's chemical forces and organized by a special detail of ss troops with the help of a field engineer battalion. chemical forces general ochsner reported to german command in june 1942 that a chemical unit had taken part in the battle. after the battle in mid-may 1942, roughly 3,000 red army soldiers and soviet civilians not evacuated by sea were besieged in a series of caves and tunnels in the nearby adzhimushkay quarry. after holding out for approximately three months, "poison gas was released into the tunnels, killing all but a few score of the soviet defenders." thousands of those killed around adzhimushkay were documented to have been killed by asphyxiation from gas. in february 1943, german troops stationed in kuban received a telegram: "russians might have to be cleared out of the mountain range with gas." the troops also received two wagons of toxin antidotes. western allies the british stockpiled chemical weapons to use in case of a german invasion. pictured is a chemical warfare bulk decontamination vehicle. the western allies did not use chemical weapons during the second world war. the british planned to use mustard gas and phosgene to help repel a german invasion in 1940–1941, and had there been an invasion may have also deployed it against german cities. general alan brooke, commander-in-chief, home forces, in command of british anti-invasion preparations of the second world war said that he "...had every intention of using sprayed mustard gas on the beaches" in an annotation in his diary. the british manufactured mustard, chlorine, lewisite, phosgene and paris green and stored them at airfields and depots for use on the beaches. the mustard gas stockpile was enlarged in 1942–1943 for possible use by raf bomber command against german cities, and in 1944 for possible retaliatory use if german forces used chemical weapons against the d-day landings. winston churchill, the british prime minister, issued a memorandum advocating a chemical strike on german cities using poison gas and possibly anthrax. although the idea was rejected, it has provoked debate. in july 1944, fearing that rocket attacks on london would get even worse, and saying he would only use chemical weapons if it were "life or death for us" or would "shorten the war by a year", churchill wrote a secret memorandum asking his military chiefs to "think very seriously over this question of using poison gas." he stated "it is absurd to consider morality on this topic when everybody used it in the last war without a word of complaint..." the joint planning staff, however, advised against the use of gas because it would inevitably provoke germany to retaliate with gas. they argued that this would be to the allies' disadvantage in france both for military reasons and because it might "seriously impair our relations with the civilian population when it became generally known that chemical warfare was first employed by us." in 1945, the u.s. army's chemical warfare service standardized improved chemical warfare rockets intended for the new m9 and m9a1 "bazooka" launchers, adopting the m26 gas rocket, a cyanogen chloride (ck)-filled warhead for the 2.36-in rocket launcher. ck, a deadly blood agent, was capable of penetrating the protective filter barriers in some gas masks, and was seen as an effective agent against japanese forces (particularly those hiding in caves or bunkers), whose gas masks lacked the impregnants that would provide protection against the chemical reaction of ck. while stockpiled in us inventory, the ck rocket was never deployed or issued to combat personnel. accidental release on the night of december 2, 1943, german ju 88 bombers attacked the port of bari in southern italy, sinking several american ships—among them the ss john harvey, which was carrying mustard gas intended for use in retaliation by the allies if german forces initiated gas warfare. the presence of the gas was highly classified, and authorities ashore had no knowledge of it, which increased the number of fatalities since physicians, who had no idea that they were dealing with the effects of mustard gas, prescribed treatment improper for those suffering from exposure and immersion. the whole affair was kept secret at the time and for many years after the war. according to the u.s. military account, "sixty-nine deaths were attributed in whole or in part to the mustard gas, most of them american merchant seamen" out of 628 mustard gas military casualties. the large number of civilian casualties among the italian population was not recorded. part of the confusion and controversy derives from the fact that the german attack was highly destructive and lethal in itself, also apart from the accidental additional effects of the gas (the attack was nicknamed "the little pearl harbor"), and attribution of the causes of death between the gas and other causes is far from easy. rick atkinson, in his book the day of battle, describes the intelligence that prompted allied leaders to deploy mustard gas to italy. this included italian intelligence that adolf hitler had threatened to use gas against italy if the state changed sides, and prisoner of war interrogations suggesting that preparations were being made to use a "new, egregiously potent gas" if the war turned decisively against germany. atkinson concludes, "no commander in 1943 could be cavalier about a manifest threat by germany to use gas." development during the cold war after world war ii, the allies recovered german artillery shells containing the three german nerve agents of the day (tabun, sarin, and soman), prompting further research into nerve agents by all of the former allies. although the threat of global thermonuclear war was foremost in the minds of most during the cold war, both the soviet and western governments put enormous resources into developing chemical and biological weapons. britain porton down was first established in 1916 and became the centre for the development of chemical weapons. in the late 1940s and early 1950s, british postwar chemical weapons research was based at the porton down facility. research was aimed at providing britain with the means to arm itself with a modern nerve-agent-based capability and to develop specific means of defense against these agents. ranajit ghosh, a chemist at the plant protection laboratories of imperial chemical industries was investigating a class of organophosphate compounds (organophosphate esters of substituted aminoethanethiols), for use as a pesticide. in 1954, ici put one of them on the market under the trade name amiton. it was subsequently withdrawn, as it was too toxic for safe use. the toxicity did not go unnoticed, and samples of it were sent to the research facility at porton down for evaluation. after the evaluation was complete, several members of this class of compounds were developed into a new group of much more lethal nerve agents, the v agents. the best-known of these is probably vx, assigned the uk rainbow code purple possum, with the russian v-agent coming a close second (amiton is largely forgotten as vg). on the defensive side, there were years of difficult work to develop the means of prophylaxis, therapy, rapid detection and identification, decontamination and more effective protection of the body against nerve agents, capable of exerting effects through the skin, the eyes and respiratory tract. tests were carried out on servicemen to determine the effects of nerve agents on human subjects, with one recorded death due to a nerve gas experiment. there have been persistent allegations of unethical human experimentation at porton down, such as those relating to the death of leading aircraftman ronald maddison, aged 20, in 1953. maddison was taking part in sarin nerve agent toxicity tests. sarin was dripped onto his arm and he died shortly afterwards. in