It is legal in Singapore to detain a person without trial. The Internal Security Act (ISA) (Singapore Statutes, Chapter 146) legalises such detention. This law was originally enacted in the Federation of Malaya in 1960 and applied in Singapore in 1963, when Singapore joined the formation of Malaysia.　Prior to the introduction of ISA in Singapore, Singapore already had similar laws to legalise such detention. These were The Essential Regulations of 1946, The Emergency Regulations Ordinance of 1948, and The Preservation of Public Security Ordinance (PPSO) of 1955. This means that it has been legal continuously to detain a person without trial in Singapore since the end of World War II, and the efforts of the local politicians to acquire a Constitution conferring the full-internal government in Singapore was pursued under the public order brought by such laws. 　This article seeks to analyse the implications of such laws for the development of the Constitution of Singapore. The intertwined relations between the aforesaid laws and the Constitution will be highlighted, and the semisovereignty of the Singapore Government of 1959 will be scrutinised.