Operation Spectrum(Chinese: 光谱行动) was launched on May 21, 1987 by Singapore‘s Internal Security Department (ISD) using the Internal Security Act (ISA).

16 people were arrested for their involvement in what was described as a “Marxist conspiracy”.

On June 20, 1987, four of the original 16 were released and six more were arrested. One of the six on June 20, 1987 was Tang Fong Har.

They were detained without trial for between one month and three years.

Tan Wah Piow, a former University of Singapore Students’ Union president residing in England was named the mastermind behind the plot.

Tan had fled Singapore in 1976 after evading National Service.

The 16 people who were arrested were
Vincent Cheng Kim Chuan,        Teo Soh Lung,
Kevin de Souza,                              Wong Souk Yee,
Tang Lay Lee,                                  Ng Bee Leng,
Jenny Chin Lai Ching,                   Kenneth Tsang Chi Seng,
Chung Lai Mei,                                Mah Lee Lin,
Low Yit Leng,                                  Tan Tee Seng,
Teresa Lim Li Kok,                        Chia Boon Tai,
Tay Hong Seng                                William Yap Hon Ngian.

The mostly English-educated group was a mix of church workers, social workers, graduates and professionals who were arrested and accused of being part of a Marxist conspiracy to topple the PAP-ruled government.

Their intention was to “subvert Singapore’s political and social order using communist united front tactics“.

Vincent Cheng, a full-time church worker was alleged as Tan Wah Piow’s key assistant. They supposedly shared a common goal of establishing a classless society.

By December 1987, all the detainees had been released except for Cheng.

However, in April 1988, nine of the released detainees issued a joint statement accusing the government of ill treatment and torture while under detention. They also denied involvement in any conspiracy and alleged that they were pressured to make the confessions.

Eight of the nine were re-arrested and detained for a second time.

The ninth member, Tang escaped re-arrest as she was in the United Kingdom.
(Tang was served with a one-year detention order under the ISA. Three months later, on September 12, she was released under a Suspending Order of Detention.

This stipulated the conditions of her release. In particular, she was not allowed to ‘travel beyond the limits of Singapore without the prior written approval of the Director of the Internal Security Department’; she was not allowed to be a ‘member of any society within the Societies Act, Cap 311, or in any way to assist in the activities of any society, except with the written consent of the Director of the Internal Security Department’; she was not allowed to ‘associate with or take part in, or in any way assist in the activities of any organisation which through its publications, statements or other activities, has shown itself to be used in propagating Marxism or Communism.’

On March 7, 1988 she was allowed to visit for one month, her husband, Peter, a British subject living in Britain. On April 18, 1988, she signed a joint statment with the other 8 ex detainees, but escaped re-arrest as she was in Britain

Tang is now residing in Hong Kong with her husband and their son Stirling)

They were later released on condition that they sign statutory declarations denying everything they had said in their earlier press statement.

Lawyer and former Solicitor General Francis Seow, stepped in to represent one of the detainees who had sought his legal assistance. When Seow arrived at the detention center, he himself was detained by the ISD and was not released for more than two months.

He was later charged and convicted in absentia for tax evasion. Seow now lives in exile in the United States.


May 1987 : Sixteen persons are arrested under the ISA. Government says detainees are involved in a Marxist conspiracy.

Jun 1987 : Lee meets Archbishop Yong and Catholic leaders. Four of the original 16 detainees are released. Six more people are arrested.

Sep 1987 : Teo and six others are freed.

Dec 1987 : All detainees freed except for Cheng.

Apr 1988 : Nine detainees issue statement denying involvement in Marxist plot and alleging ill-treatment while under detention. Eight are re-arrested. Teo files writ of habeas corpus.

Jun 1988 : Four more detainees freed. Teo, Tsang, Wong and Kevin de Souza are issued with one-year detention orders. They begin habeas corpus proceedings.

Aug 1988 : Teo’s habeas corpus dismissed. She files appeal to Court of Appeal.

Sep 1988 : Appeal is heard.

Dec 1988 : Court of Appeal orders four detainees released but are re-arrested immediately.

Feb 1989 : Two more detainees freed.

Mar 1989 : New writ of habeas corpus hearing on Teo’s re-detention. Three other detainees withdraw their writs and are released.

Apr 1989 : Teo’s habeas corpus application is dismissed. She appeals.

Jun 1989 : Detention orders for Teo and Cheng extended for one year. Cheng files writ of habeas corpus.

Feb 1990 : Cheng’s application is dismissed.

Apr 1990 : Teo’s appeal is dismissed.

Jun 1990 : Teo and Cheng are released.

Conflict between State and Church

In the plot, the Singapore government charged that Vincent Cheng, a full-time church volunteer was Tan Wah Piow’s key assistant. Cheng, who once studied to be a Catholic priest concentrated on two main areas – church groups and students via the student union, especially those of Singapore Polytechnic.

The strategy was to use the church as a front in their political struggle. During small Bible study sessions, Cheng and his members spread Marxism and anti-establishment ideas.

The government listed church organisations that it believed were used to further the Marxist cause.

This included the Justice and Peace Commission, of which Cheng was the executive secretary, the Student Christian Movement of Singapore, the Young Christian Workers Movement and the Catholic Welfare Centre, which assisted foreign workers and maids working in Singapore.[3]

It was also said that the detainees had links with Filipino leftists and advocates of liberation theology” as well as Sri Lankan separatists. Liberation theology or Christianised Marxism, began within the Roman Catholic church in Latin America in the 1950s–1960s as a moral reaction to the poverty caused by social injustice in that region. However, elements of liberation theology was strongly criticized by the Vatican during 1984-1986 after it was used for political ends where sins of the individual were transferred to institutions.

Following the Marxists arrests, Catholic priests Fathers Edgar D’Souza and Patrick Goh issued statements questioning the detentions. Church services were held for the detainees and their families and this led to the build-up of tension between the Church and the government. A meeting was arranged between Prime Minister Lee Kuan Yew and the head of the Catholic Church in Singapore, Archbishop Gregory Yong and several other Catholic Church representatives. Lee’s prime concern was that there should not be any conflict between the Church and the State because of the arrests.

The group was shown documents relating to Cheng, which included letters, and meeting notes in Cheng’s handwriting.

 Archbishop Yong said that he accepted the Internal Security Department’s (ISD) evidence against Cheng and was convinced that the government had nothing against the Catholic Church when they arrested him. Lee stressed that the government upheld freedom of religion but will not tolerate the use of religion for subversive activities.

In a move to avoid conflict, Fathers Joseph Ho, Patrick Goh, Edgar D’Souza and Guillaume Arotcarena resigned from all positions in church organisations. Archbishop Yong later suspended them from their preaching duties and warned the clergy not to mix politics and religion. He also announced that the Catholic Centre for Foreign Workers would be shut down

The re-arrests of 1988

With the exception of Vincent Cheng, all the above detainees were released, on various dates, before the end of 1987.

On 18 April 1988, nine ex-detainees issued a joint public statement (see below) repudiating earlier confessions and alleging ill-treatment by ISD officers while in detention.

Eight of whom –
Tang Lay Lee, Kenneth Tsang,
Teo Soh Lung, Ng Bee Leng,
Chng Suan Tze, William Yap Hon Ngian,
Wong Souk Yee and Kevin De Souza –

were re-arrested the next day. The ninth member, Tang Fong Har, escaped the re-arrest as she was overseas at the time, and has remained in exile to this day.

Also arrested was lawyer Patrick Seong, whom the government accused of having been a “propagandist” in providing information to foreign correspondents during the 1987 detentions.

Ten days later, the government announced that a proposed commission of inquiry into the allegations made by the detainees was no longer necessary as the signatories have since recanted their statement while in detention.

On 6 May, Francis Seow, while waiting to meet two of the detainees, was himself arrested within the premises of the ISD. The government accused him of “colluding with U.S. diplomats to build an opposition in Singapore.”

Arrested two days later was Chew Kheng Chuan, who was not among the signatories but had allegedly helped edit, printed and distributed the statement.

Most of the detainees were released in stages in late 1988 and throughout 1989, after signing statutory declarations recanting earlier allegations.

Teo Soh Lung, who had chosen to take her case to court, was held until 1990. Vincent Cheng was the last of the “Marxist conspirators” to be released, shortly after Teo.