In each game I've played (xbox 360) it does nothing as far as I can see, perhaps it's working but you can't actually see it?
Has anyone else experienced this?

It works(on playstation at the least), but it has a very short range, how close is the target when it's not firing?

I thought it had the same range as the other defensive weapon on the jsf tank, if it has a shorter range then perhaps i'm wrong

Other defensive weapon? I thought that was the only one...or do you mean the the machine gun mounted along side the main cannon? That's a offensive weapon.

No, I mean defense 4 which is some sort of close range machine gun mounted on top of the tank

Was defense 4 an upgrade for the defensive weapon? Don't remember there being two, but I do know my fully upgraded legendary tanks defense weapon did work, but at very short range.

defense 4 only adds DAMAGE to the auto grenade launcher and the ones on my tanks works fine and about half the range of my main cannon...

only 3 damage inducing weapons on the tanks:
main gun
coaxial gun(along side main gun)
auto-grenade launcher

there is no other weapons you get for the tanks that are visible to the player so i dont know is you have something different on the 360 tanks or your tv is messing up you eyes lol

oh ok that clears things up, I just thought that defense 4 was a different weapon, because to me it doesn't look like a grenade launcher.

the JSF Tank Auto-Grenade Launcher does nothing

it flies out the side of the armor and misses its target.

it doesnt even try to turn to hit the target!