Salarian dreadnoughts ( lit. "fortress ship", but more accurately "protected vessel"). These were floating bastions that needed to be towed into position by smaller craft where they'd theoretically dominate everything around them with their superior firepower. Given the geography of Sur'Kesh, there have been instances in their early modern history where these things were dragged across shallow polders and wetlands and then sunk into the beds as a sort of mobile, instant fortification, usually to the frustration of any ambitious dalatress with designs on the area. Much like with their modern doctrine regarding dreadnoughts, the salarians never considered these things very practical or worth the expense.