Saturation Salvo timing window

[iaco]

I would like to know at what time during the attack phase should I spend the additional charge for Saturation Salvo.
The card reads: while performing an attack. Does it mean that I spend the additional charge before I roll the attack dice, after I rolled the attack dice, or after the opponent has rolled the defense dice?
Thank you in advance

[Tim H]

The timing window for Saturation Salvo is in step 3B (Modify Defense Dice). The Defense Dice are rolled in step 3A and then during step 3B the attacker first has the opportunity to modify the defence dice and it is at this point you would spend the charge and choose the defence dice to be rerolled by the defender.