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The Sarin Gas Attacks on Tokyo Subway in 1995 Case Study

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Updated: Jul 23rd, 2020


Terrorism has become one of the most dangerous security threats facing modern society. In most cases, terrorists have made use of conventional weapons to carry out their terror attacks. However, there have been instances where terrorists made use of unconventional weapons. The most prominent incident involving Weapons of Mass Destruction was the Tokyo Subway Attack of 1995. Hoffman (2007) reveals that the Tokyo sarin attack is “the largest nerve agent exposure of a civilian population to date” (p.607). This attack is the most significant terror attack to be carried out in Japan in modern history. A religious terrorist group carried out the attack effectively demonstrating how terrorists could use biological weapons to devastate the population. This paper will provide a history of the sarin gas attack on the Tokyo Subway and highlight the security issues that the incident raised. It will then show how the issues were resolved to make Japan safer from terror.

Perpetrators of the Attack

The terrorist group responsible for the attack was the Aum Shinrikyo, which translates to “the Supreme Truth Religion”. This cult was founded by Shoko Asahara in 1987 and it was based on an apocalyptic view of the coming millennium (Haberfeld & Hassell, 2009). Asahara regarded himself as “today’s Messiah and Savior of the century”. As the charismatic leader for the cult, Asahara had absolute power and demanded unquestioning devotion from his followers. The cult believed that an Armageddon was coming and that the cult members would be the primary leaders and survivors of this apocalypse.

While initially a non-violent sect, the group became violent following the failure of its leader to win an election. After this failure, Asahara stated that a major goal for the cult would be to “punish the world and speed the Armageddon necessary before the world’s salvation” (Haberfeld & Hassell, 2009, p.223). Asahara declared that the cult needed to acquire the most powerful weapons needed to take part in the nearing Armageddon. The Aum set up laboratories where the cult members from various scientific fields engaged in research into biological weapons. This scientific research led to the production of sarin for use in a biological attack on the subway system

The attack was intended to cause the greatest amount of fear and destruction. Aum hoped to create the greatest number of casualties and begin the Armageddon that the sect believed in. The terrorists choose the rush hour to instigate their deadly attack against the passengers. Haberfeld & Hassell (2009) assert that the terrorists chose densely populated trains to poison as many people as possible once the chemical substance was released. To the sect members, making Armageddon a reality would ensure that the legitimacy of the Asahara, the cult leader, would be affirmed forever.

The Attack

The Tokyo attacks took place on March 20, 1995, when terrorists used WMD to attack the Tokyo subway system. The attack was carried out by members of the religious sect Aum Shinrikyo. The weapon of choice by the terrorists was sarin gas. Sarin gas is an extremely lethal substance and it has no recognized purpose other than wounding or killing people (Dilip & Kratcoski, 2003). Sarin gas (methyl phosphonofluoride isopropyl) was discovered by German Chemists before the Second World War. When exposed to people, this gas is absorbed through the skin and respiratory organs. It causes symptoms such as vomiting, headaches, pupils-contraction, respiratory difficulties, and internal organ complications that can lead to death.

How the Attack was carried out

The gas was released at several points in the Tokyo subway system to ensure that the effects were widespread. The members involved in the execution of the attack had been well prepared for their roles. Each terrorist entered into one of five subway trains with a packet containing the poisonous gas sarin (Dilip & Kratcoski, 2003). These packets were well hidden in unsuspicious items such as lunch boxes and soft drink containers. Once onboard the subway cars, the terrorists placed the packets containing sarin on the floor of the train and concealed the packets using newspapers. The terrorists then put on gauze surgical masks and punctured the sarin bags using umbrella tips. After this, they quickly exited the trains leaving behind the punctured sarin packets releasing toxic gas into the trains.

Once the poisonous gas had been released, the subway users did not realize that an attack had been carried out. Sadayoshi (1997) explains that sarin is a colorless, odorless and highly lethal organophosphate compound. It was therefore impossible for the passengers to detect the presence of this toxic substance in the air. Haberfeld and Hassell (2009) document that while the effects of the gas were immediate and some passengers started suffering as soon as the gas was released, it was not apparent that a terrorist attack was taking place. The trains continued on their routes even as more passengers continued to suffer from the effects of the poison. More than one hour after the gas had been released the trains were evacuated.

Impacts of the Attack

The attack led to the death of 11 people and the injury of over 5,500 people (Hoffman, 2007). A major problem in the Tokyo incident was that it took a while for the subway authority to recognize the problem (Dilip & Kratcoski, 2003). The trains continued to operate as usual even after the sarin gas had been released and passengers had started to suffer from its impact. The sarin agent was not identified until 9:27 am even though it had been released at about 8:00 am. The delay in problem recognition led to more destruction by the attack.

There was a poor response from the police and emergency agencies in Tokyo. To begin with, these agencies took time in identifying the problem. They did not respond appropriately to the tragedy since although calls to the police were made shortly after the attack, the decision to stop the trains was only reached about 1.5hours later. The law enforcement agencies also failed to share information about the nature of the attack with other emergency organizations (Dilip & Kratcoski, 2003). This lack of information sharing had detrimental effects since the emergency responders did not take the necessary measures to protect themselves from the toxic agent.

Critics of the government argued that the attack could have been averted if the state authorities were more effective. Members of the Aum had carried out a sarin gas attack in the small mountain town of Matsumoto in June 1994 (Dilip & Kratcoski, 2003). This attack had killed seven people but investigators failed to connect the incident with the religious sect. Instead of identifying the sarin gas incident as a terrorist attack, police officials designated it as an accident.

Solutions to the Security Issues

The Tokyo attacks demonstrated that subways were a realistic target of terrorists. Before this attack, governments had considered the implications of a terrorist attack against the subways. However, the danger of such attacks had never been properly quantified. Haberfeld and Hassell (2009) reveal that following the Tokyo attack, the danger and the possibility of subway attacks using a biological weapon was shown. This attack made the risk of subway attacks an urgent and practical issue for many governments. Policymakers had to identify and implement ways to protect or minimize the risk of subway terrorism in their respective countries.

The Tokyo attack highlighted the problem of the lack of information sharing among Japanese law enforcement agencies. This problem made the agencies highly ineffective when dealing with the terrorism issue. Following these attacks, the issue of inter-prefectural police rivalries was addressed. Measures were taken to ensure that good information sharing practices were adopted within the security apparatus. After the Aum attacks of 1995, the Japanese Police Law was amended to allow police to cross-prefectural boundaries when dealing with terrorist groups (Alperen, 2011).

A major effect of the Tokyo Subway attack was that it demonstrated that Japan was vulnerable to terrorist attacks. The local and national officials were unprepared for a biological attack in 1995. Alperen (2011) states that the local authorities were ill-prepared to properly respond to any type of terrorist attack on the country. The attack led to the development of an effective response mechanism to chemical terrorist attacks in Japan. The newly formulated system had a set of procedures and response mechanisms tailor-made for biological weapons attacks (Alperen, 2011). They included specially trained medical personnel who could deal with mass casualties and decontamination teams that could be deployed promptly. Plans were also made for evacuations and quarantining in the event of a chemical attack. In addition to this, the efficacy of the public emergency notification and warning system was greatly improved.

The Tokyo attacks led to the amendment of the Religious Corporation Law of 1951 to give police greater powers when dealing with groups suspected of terrorist activities. Before the Tokyo attacks, religious groups and individuals enjoyed many freedoms. According to Alperen (2011), religious groups could operate with little government interference since the Religious Corporation Law of 1951 placed huge restrictions on government intrusion into the affairs of officially recognized religious organizations. The Aum Shinrikyo was able to exploit this privilege to carry out unlawful activities such as experimentation with biological weapons. After the attacks, the law was amended to make it possible for law enforcement agencies to investigate suspected terrorist groups and avert future crises.

A major step undertaken by the government was to increase monitoring of the activities of groups that might have a terrorist motive. The government increased restrictions to ensure that religious groups could not engage in activities such as the development of weapons unnoticed. In the years following the Tokyo attacks, surveillance on suspected cults was increased to minimize the risk that any group might pose to the security of the population (Dilip & Kratcoski, 2003). With increase surveillance, organizations can no longer engage in the kind of research with military purpose that Aum Shinrikyo members were able to.


This paper set out to discuss the Sarin attack against Tokyo’s subway system in 1995. The paper has revealed that this attack was undertaken by the Aum religious sect under the guidance of its leader, Shoko Asahara. The attack was the first significant terrorist attack on Japan in modern times. The country was unprepared for this attack and this led to higher destruction. The paper has illustrated how, because of the Tokyo attacks of 1995, the Japanese government took steps to prevent such terror attacks in the future or prepare adequately for response against such nonconventional attacks.


Alperen, M. (2011). Foundations of Homeland Security: Law and Policy. NY: John Wiley & Sons.

Dilip, D., & Kratcoski, P. (2003). Meeting the Challenges of Global Terrorism: Prevention, Control, and Recovery. London: Lexington Books.

Haberfeld, M.R. & Hassell, A. (2009). A New Understanding of Terrorism: Case Studies, Trajectories and Lessons Learned. Boston: Springer.

Hoffman, A. (2007). A Decade after the Tokyo Sarin Attack: A Review of Neurological Follow-Up of the Victims. Military Medicine, 172 (6), 607-610.

Sadayoshi, O. (1997). Sarin Poisoning on Tokyo subway. Southern Medical Journal, 90 (6), 587-593.

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