One of the 320,000 who registered as citizens under the Singapore Citizenship Ordinance of 1957 was the late grandfather of historian Seng Guo Quan of the National University of Singapore.
Mr Seng Chek Hong was born in 1916 in Guangdong, China.
He arrived in Singapore as a 17-year-old in 1933 with his mother, and lived in the Beach Road area with relatives.
He was a grocer at the old Beach Road Market for over three decades, until he stopped working in the 1970s due to ill health.
In 1957, after the passing of the citizenship ordinance, he registered as a Singapore citizen, renouncing his Chinese citizenship.
His Singapore citizenship certificate is dated Dec 23, 1957.
"According to my grandmother, people hesitated when the citizenship was offered. They must have, since it took them till December to register," says Dr Seng. The registration drive began on Nov 1, 1957, and ended on Jan 31, 1958.
Dr Seng was born in 1981, five years after the death of his grandfather. His knowledge of his grandfather was passed down from his grandmother Goh Whee Kheng, who is alive and aged 87.
He said of his grandfather: "Like the Chinese masses, he was most likely sympathetic of the left wing. There are stories of him sending vegetables and food to the Chinese High students who were barricading themselves in school (during a demonstration) in 1956."
"My grandmother also remembers him telling her to vote for the 'lightning symbol', most likely in 1959," adds Dr Seng, referring to the symbol of the People's Action Party, which took power in a shock landslide victory during the 1959 General Election.
Mr Seng Chek Hong died in 1976, leaving behind five children and one granddaughter.
He was cremated and his urn was placed in the Tse Toh Aum Temple in Sin Ming Drive.
Dr Seng says his grandfather's story marks a break with the "sojourner mentality" of previous generations, who would travel back and forth between China and Singapore. Mr Seng Chek Hong never went back to China after leaving in 1933.
The citizenship offer in 1957 was one factor that helped many China-born Chinese make up their minds to sink roots in Singapore, he notes - the other factor was China coming under communist rule in 1949.