SINGAPORE - Their two sons' national service (NS) obligation was the last thing on the mind of Senior Counsel Tan Chee Meng and his wife when they made the difficult decision for the family to migrate to Canada in 2000.

He said the couple had decided that moving to Canada was in the best interest of the children, adding that "NS was the last thing on our minds, let alone evasion".

But his two sons decided on their own in 2015 that they wanted to serve NS, a decision that the father said he is "very proud of".

The decision has led to both sons - Jonathan Tan Huai En, 28, and Isaac Tan Yang En, 25 - being convicted and receiving jail sentences this year for defaulting on NS.

The younger son was sentenced on Wednesday (Oct 11) to 12 weeks' jail for evading NS for about six years while the elder son was sentenced to 16 weeks' jail in February for a similar offence involving a 10-year default period.

In a media statement issued after the sentencing, Mr Tan said he takes responsibility for what happened and that the law has to take its course.

"As a father, it is heart breaking to see my sons go to jail in circumstances such as these. I take responsibility for what happened and the law has to take its course," said the father, deputy chairman at WongPartnership law firm.

"The past 2½ years have not been easy but we will get through this as a family."

Isaac Tan, who is now serving his NS and will complete it later this month, had pleaded guilty on Oct 6 to one count of remaining outside Singapore without a valid exit permit.

A second charge for a similar offence and one count of failing to comply with a Further Reporting Order to report for NS registration, pre-enlistment documentation and medical screening were taken into consideration during sentencing.

Deputy Public Prosecutor Tan Zhongshan told the court on Oct 6 that Isaac Tan is a Singapore citizen by birth.

On Dec 1, 2000, Isaac Tan had migrated to Canada with his mother, older sister and brother. Their father remained in Singapore because of the lack of employment opportunities overseas.

Isaac Tan received his Canadian citizenship in early 2005.

The court heard that on Sept 8, 2009, his father's lawyers wrote to the Central Manpower Base (CMPB), requesting that Isaac Tan's NS be deferred until he turned 21, when he intended to renounce his Singapore citizenship.

The CMPB replied later that month, rejecting the request.

DPP Tan said: "CMPB also stated... that the accused had been remaining outside Singapore without a valid exit permit, and the accused should return to Singapore to resolve his NS offences as soon as possible in order not to prolong his default period."

Isaac Tan returned to Singapore on Aug 6, 2015, and enlisted in full-time NS about two months later.

DPP Tan said Isaac Tan had been aware of his NS obligations for years and urged District Judge Marvin Bay to sentence him to at least three months' jail.

In his sentencing remarks on Wednesday, District Judge Bay stressed NS is a critical obligation and cannot be relegated to a task to be performed at a time of an individual's own convenience.

He added: "Punishments for NS defaulters must be sufficiently severe and appropriately calibrated so as to deter any potential offenders from either gaming the system, or forming any notion that the reward... for postponing their NS obligations - for example, to complete an overseas degree - can possibly outweigh the costs of their eventual punishment in our courts."

The judge noted that Isaac Tan had "persisted to remain in Canada" until August 2015, after he had completed his university studies.

He said: "There was no evident urgency on (Isaac Tan's) part to return despite being told on Oct 7, 2014, that he had been classified as an NS defaulter and was directed to return to Singapore to respond to his offences, and of course, fulfil his outstanding NS obligations."

In mitigation, Isaac Tan's lawyer, Ms Josephine Choo, said her client had come back to Singapore for the sole purpose of fulfilling his NS obligations.

Pleading for a five-week jail term, she also said he suffers from atopic dermatitis, a type of eczema, and needs regular follow-up treatments.

Isaac Tan's brother, who remained abroad without a valid exit permit between Dec 22, 2004 and May 4, 2015, surrendered himself to the State Courts on Oct 6 to begin serving his sentence.

Offenders convicted of remaining outside Singapore without a valid exit permit can be jailed for up to three years and fined up to $10,000.

In July, the High Court laid down fresh sentencing benchmarks for NS dodgers.

The three-judge panel, led by Chief Justice Sundaresh Menon, set out four sentencing bands based on the length of default.

For those who evade NS for two to six years, the starting point is two to four months in jail; for seven to 10 years, it is five to eight months in jail; and for 11 to 16 years, it is 14 to 22 months in jail.

For the worst cases involving those who evade their duty for 17 to 23 years or more, the default jail term kicks off from two years to the maximum of three years in jail.