Tactics for playing as the Dwarves.

Hello everyone! Could you please advise when it's best to attack the Dragon Utopia while playing as the Fortress faction? What's the minimum number of troops needed to defeat the dragons without significant losses? Which hero skills and battle tactics will make taking the Utopia easier? Thanks in advance! P.S. I'm very interested in reading your forum; it's great that Heroes of Might and Magic V is still popular!