work, and being a medical frontliner are also activities seen as contributing to civil defence. Economic defence Economic defence relates to governmental efforts to sustain and develop Singapore's economy, while a policy is undertaken by the government for workers to upgrade their skill sets. The Singapore Government also stockpiles essential supplies of food, medication and personal protective equipment, in addition to pursuing secondary supply chains, so as to offset potential disruptions. The conservation of essential resources including water is placed under economic defence. Social defence Social defence stems from official policies to maintain social cohesion among Singapore's diverse population through multiculturalism. As part of state-backed efforts, religious leaders engage in interfaith sessions through the Inter-Religious Organisation; such efforts are seen as necessary by the Singapore Government to counter non-state actors influence operations. Improving relations between neighbours is also listed as part of social defence. Psychological defence Psychological defence refers to the Singapore Government's programme to strengthen "resolve and resilience" amongst its citizens to face unexpected crises; it is also cited as necessary to combat fake news. The government views psychological resilience as the bedrock of a "social compact" and seeks to emulate Finland's example. Efforts to improve mental health in Singapore is also placed under psychological defence. Digital defence Digital defence refers to efforts to increase awareness of online security threats, including misinformation, cyberattacks and phishing scams. The threat is seen as particularly acute due to the country's "open and connected" nature and governmental plans to orientate the country around a digital economy and the Smart Nation concept. All civil servants are mandated to undergo cybersecurity training, with the government also increasing audits of state infrastructure. Commemoration Total Defence Day Total Defence Day was added to the list of dates for schools to commemorate on 17 May 1997, and first nationally marked on 15 February 1998 with the Singapore Civil Defence Force sounding the Important Message Signal through the island-wide Public Warning System sirens and local radio stations for a minute. The date was chosen to mark the British surrender of Singapore to Japan during World War II. At its inception, the siren was sounded at 12:05pm Singapore Standard Time; this was changed to 6:20pm in 2015 to mark the actual time of the surrender in 1942. Schools conduct emergency preparedness drills, food and electricity rationing, and may organise tours to government exhibitions. The defence minister also delivers an address