open up your primitives, make a box, make another box (name it turret01), slap it on as a child. Save the model, then run it through a cob -> pof converter (kazan made one), open it (the pof) with MODELVIEW32 (decent-network), stick a firing point on that new subobject. Make a new table entry by copying an old cruiser, replace the pof name of the cruiser with your pof (dump the pof in /data/models), and take off all the turrets except one. Give it a ULTRA Anti-Fighter Beam, throw it in a mission, beam-free-all it, and get destroyed by your own ****ty creation.
~time to make: 5 minutes.