CD for units

Hi everybody. I came up with the idea that, there should be a timer for artillery types units( battleships, railroads,..) when they are not in battle to see when they be ready for their next shot. For example, when I shoot and run away, I wonder when can I prepare for the next fire to dodge the enemy fire. there should a kinda timer like the units are in the battle that shows you when is the next fight, so it shows you when you are out of range and are not in a battle or firing.