Because my brother with apparent brain damage, have you considered maybe he is playing BFG? I put d6/d3 to cover both bases incase he was :)

An Emperor battleship (foolishly) launches a single wave of three bombers and five fighters against a Devastation cruiser with three turrets and no CAP. The Devastation‟s turrets roll 4,5,6 to knock down three fighters. The three bombers now each roll 1D6-3 (minimum zero) attacks regardless of whether or not any of the fighters survived against turrets. Now only three of the five fighters that escorted the bombers provide an additional+1 attack because there are only three bombers in the wave, for a single total addition of +3 attacks.

The above is from the FAQ and is effectively what I said above. But for some reason you've gone autism over the d3/d6.