There's not a big US base. I used to be stationed there. There is a logistics command, CTF-73, and more recently (past decade) some LCS rotational crews call Sembawang/Chagi Naval Base home. Singapore owns the wharf where the logistics command resides, as well as the old black and whites used by the US military.

To your point of it being intended for Indonesia over Malaysia, that could be the case. I was going off of heresay about Malaysia being the threat . It seemed plausible since some sensitive positions are still off-limits to Singaporean-Malays during their NS.