The move to match interests with national service vocations is a good step forward, but the young men heading for enlistment will also have to manage their expectations, defence experts said.

This is because operational requirements are still paramount, meaning enlistees may be posted to less popular vocations if that is where soldiers are required.

For example, said associate professor Bernard Loo, a defence analyst at the S. Rajaratnam School of International Studies (RSIS), there is always great demand for infantry.

"If you look at the army alone, the reality is that the single greatest human resource requirement is in infantry," he said. "I don't think you're going to escape from that reality anytime soon."

In his annual interview leading up to SAF Day yesterday, Defence Minister Ng Eng Hen announced that, for the first time, new enlistees will get to indicate which vocations they would want to serve in. The change will kick in from the end of next year.

Their preferences will be taken into account after they are posted to the Singapore Armed Forces (SAF), police or civil defence.

But he said operational needs remain the main consideration when postings are being made.

Mr David Leong, who is managing director of PeopleWorldwide Consulting, said that a recent discussion he had with polytechnic students showed that their interests geared towards the "sexier" parts of the SAF - like the air force.

"(The move) shows that the Government is listening, but now with that expectation you will also have some disappointment," he said.

Mr Vikram Nair, chairman of the Government Parliamentary Committee for Defence and Foreign Affairs agreed that not everyone might get what they expressed interest in.

He said: "In my own time, I think at some time in Officer Cadet School, we were asked to pick which of the vocations we wanted, but the reality was that the largest manpower needs were infantry and most of us were going there regardless of what we picked."

Defence analyst Ho Shu Huang, an associate research fellow at RSIS, said the new system is an improvement upon the current one, which "only factors in aptitude and not interest".

"That said, this initiative will unfortunately be a black box - it is hard to see to what extent indicating a preference will have on an enlistee's eventual posting as that will still largely be determined by manpower requirements," he said.

He stressed that it is important for the authorities to build public trust in the efforts they take to accommodate every individual's preference. "If such trust isn't built, the whole process could be dismissed as mere lip service," Mr Ho said.

While a number stressed the need to manage expectations, teens heading for the army liked the idea of having a choice.

Sixteen-year-old Tan Aik Wen, who is likely to be among the first few affected by the changes, said: "I think it'll have a positive impact on the kind of output the SAF will see as well in terms of productivity and morale."

• Additional reporting by Rei Kurohi