Indonesia can launch Hamas type war.
1) Launch pirate navy. Raid ships on straits of malacca using
small boats arm with anti aircraft guns. Disrupt trade routes to
Spore.
2) Launch rocket boats like what Iran did in 1980s to target
bigger ships such as oil container ships and ships carrying
chemicals.
3) Buy cheap russian submarines. Have 36 of them. Give singapore
frigates a headache to hunt them down. Submarines hunt in small
wolf packs to destroy singpore trade routes. Submarines oso launch
small armada of commandoes to go raid the island
4) Build and enhance Scuds on mobile launchers. Shoot Singapore
with Scuds. And when Singapore try to hunt down the mobile
launchers, the launchers can be driven to hidden bunkers in Riau,
Sumatra and Java.
5) Buy Soviet anti aircraft guns and SAM batteries and radar
equipment
I see only point 1 as a possibility