Why were James and John called the sons of thunder?

Another answer from the communityWe are not told this, but presumably they were 'loud' people. Perhaps as fishermen they had to shout across the water, or from water to shore or vice-versa. They may have had naturally loud voices or learned how to project their voices. It is also possible they were a little hasty to be angry with others, such as when they wanted to call the fire of God down on Samaria.