To perform an attack, the target (either hull zone of a ship or squadron) must be inside the attacking hull zone’s firing arc. In addition, the defending hull zone must be at attack range.
The attacker uses the range side of the range ruler to determine line of sight and the range to the chosen hull zone. Each range band on the ruler depicts which colors of attack dice he can roll.
For example, at long range a ship can roll only its red attack dice. If the attacking hull zone does not have any red dice, then it cannot perform this attack. (Like the CR90 B in the picture.)