It's warfare. Possibly (probably ?) against Singapore itself, or a supporter of Singapore's policy. Or to influence Singapore's policies.
Without a weapon, you have no threat.
With a weapon, you can begin to make threats.
With a credible weapon (and quantities and the people and supplies and logistics to make it a credible weapon) you can begin to decide who and what threats you can execute.
(Would Obama EVER even threaten (much less actually use force against!) anybody who is trying to oppose a Communist or Muslim or African dictator?)
In a war with Singapore, Malaysia wouldn't stand a chance. The only chance Malaysia's submarines would have is if they parked them somewhere in the middle of the Atlantic.
Meanwhile, no word on how the surfacing went...