SINGAPORE - The threat has changed but not the need to guard against it.

Thus Total Defence Day is marked every Feb 15 as a reminder that on this same day in 1942, Singapore fell to the Japanese.

Singaporeans can learn about ordinary people who have made a difference to Total Defence at an exhibition jointly organised by Nexus, the Ministry of Defence's Central National Education Office and S'pore Discovery Centre.

The focus of Total Defence has shifted from conventional warfare and rallying the nation around the Singapore Armed Forces to non-conventional threats and personal responsibility.

Dr Maliki Osman, Senior Minister of State for Defence and Foreign Affairs, said in his opening address: "We need to work hard to further strengthen our social and psychological defences."

He named terrorism as the biggest threat facing all countries, noting that "the real battle of today and of the future is for the hearts and minds of our people".

Strengthening social resilience is about building relationships between Singaporeans of all races and religions where there is proper understanding and trust. This will help to create the necessary safeguard for Singapore where Singaporeans will alert the authorities of people they know who are being radicalised.

Dr Maliki cited the example in 2013 where a post-secondary school student became self-radicalised and intended to carry out violent attacks but was fortunately stopped by a friend who alerted the authorities.

Furthermore, online space and social media has become a new battleground which terrorist groups such as the Islamic State of Iraq and Syria have utilised to recruit followers. Dr Maliki said social resilience also means rejecting messages that seek to incite hate and discrimination on new media.

Beyond the usual commitment by the armed forces, Dr Maliki also called for more individuals to volunteer their time and effort to help strengthen public support for defence.

The renewed focus on individual responsibility underpins the Total Defence Exhibition, which features 16 different inspiring stories on individuals who have played a role in Total Defence. This includes photographer Lim Xiangyun, 26, whose work to start a campaign raising more than $60,000 to clean and renovate the flats of elderly Singaporeans strengthens the social fabric - and hence defence.

The exhibition is at two locations: the Future of Us exhibition in Gardens by the Bay and the S'pore Discovery Centre. Both are now open to the public and the former is open until Feb 18 while the latter is open until March 19.

At 6.20pm on Monday (Feb 15), the Public Warning System (PWS) sirens sounded to mark the time and day the British surrendered to the Japanese Imperial Forces in 1942.

Defence Minister Ng Eng Hen wrote in a Facebook post that the siren is to "remind all Singaporeans that in our history, at this time, Singapore was lost when it could not be defended - its residents subjugated to an external power".

Other Ministers also wrote posts on the fall of Singapore, and the importance of national defence.