I've got coursework out of the way for the moment, and had this quick thought while catching up on news.
This is perhaps rather a basic question, but deterrence can't be considered in isolation. Militaries, being concerned with security, are particularly vulnerable to biased assessments of their own deterrence value. In Singapore, where the full might of the Army in particular will never be seen save full mobilization, I suspect the military is particularly prone to seeing itself as a 'doomsday weapon'.
An example of this intellectual laziness is in considering nuclear deterrence. MAD is sometimes dealt with as a field unto itself and held up as the supreme example of deterrence: the possession of nuclear weapons deters the escalation of conflicts. The destructive force of these weapons certainly went a long way in stopping superpower brinksmanship after some initial teething pains.
Still, consider a history that could have gone very differently. A Korean War where the US dropped one or two nuclear devices on the 'ChiComs' might have gotten the world used to kilo- or mega-deaths, and that the use of nuclear weapons was to be expected. Such a capability deterred war but no more than dreadnoughts or machine guns deterred war.
Such weapons made war more horrific and forced nations to build up the relevant capabilities to compete, but as soon as willingness to put lives on the line overcame merely material considerations they were moot. I won't even go into the obvious consideration that both sides of the Cold War simply sought other means to assail the other.
In the Singaporean context, Dr Bernard Loo has very simply applied the 'deterrence paradox' to Singapore multiple times - by definition it is difficult to prove that deterrence works. The pure existence of a military force does not mean that it has accomplished its mission.
To give a few other weaknesses of the argument for military deterrence; when an potential aggressor nation seeks to enforce its claims upon another, internal reasons for doing so are likely equally as important as external. Argentina pursued its claims over the Falklands partly due to the need for internal stability, and today China's claims over the South China Sea are partly motivated by internal politicking. Political scientists' models will definitely prove instructive here.
Moreover, purely military force may not be able to exercise control over overseas regions that may prove vital to national safety. For example, investment partners in the Riau Islands and Brunei provide the massively overdeveloped island city of Singapore with important materiel. As Huxley writes, it's possible that armed force may one day be deployed to protect those vital jugulars someday, but it's clear that at present political means rather than explicitly military means secure their safety.
The purpose of a military, as always, is as a useful tool discharging a variety of functions, just like a police service, fire service or education service. Even in defeat the institution of a military can serve the role of a national rallying point - see the Free French, or more recently the Kuwati military in 1991. The military does itself a disservice by overly focusing on one aspect of its existence.
Security enthusiasts ought also overcome this strategic myopia - I suspect it arises out of the inner conflict between not wanting to see the military used, yet being proud of the national project of building armed force.
