Ships of the highest ice class, 1A Super, are designed to operate in difficult ice conditions mainly without icebreaker assistance while ships of lower ice classes 1A, 1B and 1C are assumed to rely on icebreaker assistance. In addition there are ice class 2 for steel-hulled ships with no ice strengthening that are capable of operating independently in very light ice conditions and class 3 for vessels that do not belong to any other class such as barges. In official context and legislation, the ice classes are usually spelled with Roman numerals, e.g. IA. Classification societies may sometimes use somewhat different distinguishing marks for Finnish-Swedish ice classes; for example, 1A Super is defined as "Ice Class I AA" by the American Bureau of Shipping (ABS) and "ICE(1A*)" by DNV GL.