Its not just tab, you go into options for controls hotkeys etc, its about 6 tabs over in options that has targeting options.
I set tab that I don't go out of combat ever, so anything targeted my weapons autofire on(you right click the gun on your attack menu and it turns green to auto fire so you don't have to spam fire all weapons).
Anyways you set it to target anything that hits you, target off screen, and a few other things, and your ship will auto kill somethings when you can't find a target and your being shot.
Also I honestly don't use torpedo's anymore maybe 1 quantom torp in front(hits harder longer cooldown for nasty high yield 2 torpedo shots). Photon are okay, but meh. Only beam types I use are phaser, disrupter, antipoloron. Tet, pol, plasma just don't do anything. Antipoloron will crush things when you crit.