So lets say the jumpmaster can shoot a torpedo in arc to a ship, but his turret can attack biggs.

Do I have to attack biggs with the turret if I declare my torpedo as the attack?

If the person you want to shoot with the torepedo is at range 1 of Biggs then you must use your turret to shoot him rather than the ship. The FAQ for Biggs says that if you have a weapon that's able to target Biggs you must use that weapon.

Now if your turret could shoot Biggs but there is a ship beyond range 1 of Biggs that you want to use the torpedo on then fire away with that torp.

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Now if your turret could shoot Biggs but there is a ship beyond range 1 of Biggs that you want to use the torpedo on then fire away with that torp.

Otherwise known as a ship outside of the Biggs protection bubble.

If you can shoot at Biggs then any of the ships within that R1 of him are invalid targets. Ships outside of that bubble don't care about Biggs.