full-time national servicemen were deployed to provide healthcare services for patients at one of the CIFs set up in the Singapore EXPO halls. The SAF also housed about 3,000 recovering migrant workers with COVID-19 in six military camps across Singapore. The Jurong, Bedok, Amoy Quee, Guillemard, Tanjong Gul and Lim Chu Kang camps had been converted into community recovery facilities (CRFs). Operational since 28 April 2020, the CRFs are for COVID-19 patients who remain well at Day 14 of the disease and do not require further medical care. Separately, more than 1,300 SAF personnel were also deployed to make calls to do contact tracing and check compliance with stay at home notices. These contact tracers worked with Ministry of Health officials to fill gaps in the activity maps of confirmed or suspected cases. Defence Science and Technology Agency Engineers also developed tools to automate the extraction and fusion of data for analysis. The contact tracers were reported to make between 1,000 and 2,000 calls a day. Defence policy Deterrence and diplomacy have been the fundamental tenets of Singapore's military defence policy. Through the years, the military has developed extensive links with armed forces from other countries. In recent years, there has also been an increased emphasis on international peace-keeping and relief operations, notably the peace-keeping operations in Afghanistan, East Timor, the Persian Gulf and disaster relief in the Indian Ocean earthquake-tsunami of 2004, the 2005 Nias earthquake and 2006 Yogyakarta earthquake both in Indonesia, Hurricane Katrina in the United States and the 2008 Sichuan earthquake in China. According to military and strategic analysts, such as Tim Huxley in Defending the Lion City, Singapore is well poised to be using a forward-defence military doctrine. Singapore is, after all, a relatively small country of about and therefore lacks the hinterland for a defence in depth strategy. In historical news archives, there were also defence analogies used by Singapore founders that Singapore must be a poison shrimp and later, porcupine. Thenceforth, if a wartime military battle is to take place on the island of Singapore, the effects would be devastating to both the people and infrastructure. Press statements from Singapore's Ministry of Defence (MINDEF) describe the SAF as a deterrent force. The SAF's declared mission statement is to "enhance Singapore’s peace and security through deterrence and diplomacy, and should these fail, to secure a swift and decisive victory over the aggressor". Today, a