Special Submarines made to hunt Tyranno Fins. Introduced on Nilfeheim about 400 years ago. After Submarines were used during the last Clan Wars the remaining ones were destroyed or converted to Fishing and Hunting boats. Nilfeheim boats are incredibly primitve compared to Union Technology, but Subs are the few exceptions od allowed technology. Even though some argue that Hunting Subs are not "traditional".
A referendum of the Circle of Elders determined that Hunting Subs are acceptable and that they are traditional now.