SINGAPORE - The Ministry of Defence (Mindef) has set out the principles of universality and equity in national service (NS) in response to queries about the High Court's decision to impose heavier sentences on three national service defaulters.

Mindef said these principles must be upheld so as to ensure Singaporeans' important support of and commitment to national service.

"If we allow Singapore citizens who are overseas to avoid NS or to choose when they want to serve NS, we are not being fair to the vast majority of our national servicemen who serve their country dutifully, and the institution of NS will be undermined," said a Mindef spokesman on Wednesday (Apr 26).

On Tuesday, the High Court indicated that the sentences for NS defaulters should take into account the length of the default period when it allowed the prosecutors' appeal for heavier sentences for three NS defaulters.

Ang Lee Thye, 43, who evaded NS for 23½ years, had his sentence of two years lengthened to two years and nine months. He left for the United States when he was 14 and did not respond when he was told to register for national service. He reported to the Central Manpower Base in 2015 at the age of 41.

Brothers Sakthikanesh Chidambaram, 26, and Vandana Kumar Chidambaram, 23, failed to serve NS for 5½ years and nearly 3½ years respectively.

Sakthikanesh' s sentence was increased from three weeks to 10 weeks while Vandana Kumar was jailed seven weeks. He was initially fined $6,000.

Both brothers completed serving full-time NS last year.

Under the Enlistment Act, Singapore males are liable for NS from the age of 16.5 to 40.

Mindef said each case of NS evasion comes with its own circumstances which the court will consider in deciding on the sentence and added that it takes a firm stance against those who evade NS.

Mindef said of Ang: "Despite being advised to return to resolve his offences, he chose to return to Singapore at an age when he could no longer be called up for NS at all, evading his NS obligations completely."

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It said that Sakthikanesh was aware of his obligations but chose to complete his university studies in India before returning to serve NS.

Vandana was also aware he had to serve, as his father was in contact with Mindef, it said.

The two brothers had left for India when they were infants and visited Singapore occasionally.