Can you use surges to make your attack hit?

By apegod, in Star Wars: Imperial Assault

Can you use surges from attack roll to buy extra damage symbols to make your attack hit? Or, do you have to hit with dice rolled first and then you can add surges to pile on effects?

The former.

Can you use surges from attack roll to buy extra damage symbols to make your attack hit? Or, do you have to hit with dice rolled first and then you can add surges to pile on effects?

Yes. Read "Steps of an Attack" on page 5 in the Rules Reference:

sTeps of An ATTACk

When a figure performs an attack, it resolves the following steps:

1. Declare Target: Based upon its attack type (P or O), the figure performing the attack (referred to as the attacker) declares one eligible target for the attack (referred to as the target).

- For a melee attack (P), an eligible target is any hostile figure adjacent to the attacker. For a ranged attack (O), an eligible target is any hostile figure within line of sight of the attacker.

2. Roll Dice: The attacker rolls his attack dice at the same time as the defender rolls defense dice (listed under “Defense” on the target figure’s Hero sheet or Deployment card).

3. Rerolls: If players have any effects that reroll dice, they are resolved now.

- Each die may be rerolled only once per attack regardless of who is rerolling the die.

4. Apply Modifiers: If players have any effects that gain or remove icons or Accuracy, they are applied at this time. This includes spending F (evade) results to remove B results. Any B abilities that provide modifiers are not resolved until step 5.

5. Spend Surges: If the attacker has any B results, he may spend them to trigger special abilities.

6. Check Accuracy: If performing a ranged attack (O) the total Accuracy value must be equal to or greater than the number of spaces the target is away from the attacker. (See “Counting Spaces” on page 9). If the total Accuracy value is less than this number, the attack is a miss.

7. Calculate Damage: The total number of G (block) results is subtracted from the total number of H (damage) results, and then the target suffers all remaining H.