[QUOTE=Drill Bill;191868]Or would they have to be escorted by an icebreaker?[/QUOTE]
Ice classes 1A Super, 1A, 1B, 1C and II are defined in the Finnish-Swedish Ice Class Rules as follows:
[I]1. ice class IA Super; ships with such structure, engine output and other properties that they are normally capable of navigating in difficult ice conditions without the assistance of icebreakers;
ice class IA; ships with such structure, engine output and other properties that they are capable of navigating in difficult ice conditions, with the assistance of icebreakers when necessary;
ice class IB; ships with such structure, engine output and other properties that they are capable of navigating in moderate ice conditions, with the assistance of icebreakers when necessary;
ice class IC; ships with such structure, engine output and other properties that they are capable of navigating in light ice conditions, with the assistance of icebreakers when necessary;
ice class II; ships that have a steel hull and that are structurally fit for navigation in the open sea and that, despite not being strengthened for navigation in ice, are capable of navigating in very light ice conditions with their own propulsion machinery;[/I]
1A and 1A Super are roughly equal to PC-7 and PC-6, respectively. However, even the lowest polar classes take into account the possibility of encountering multi-year ice which does not occur in the seasonally freezing Baltic Sea.
Note that the winter navigation system in the Baltic Sea is based on icebreakers operating in the region. Even ships with the highest ice class are not assumed to be capable of independent icebreaking - instead, they can operate independently in broken ice channels previously opened by icebreakers. In particularly harsh winters, even these ships sometimes have to rely on icebreaker assistance. Ships of lower ice class are often towed even on easy winters, and thanks to the upcoming EEDI regulations this will likely increase in the future as the installed power on mechant ships will become smaller and the bow geometry becomes less efficient in ice.
As for icebreaker escort, having an icebreaker in front of you does not mean that you can sail with no regard of ice. This is particularly interesting when the Russians are proposing high-speed trans-polar convoys led by massive nuclear-powered icebreakers. The ice blocks surfacing in the channel behind the icebreaker would have a thickness of 2-3 metres and they would be thrown against the bow of the following ship by the icebreaker’s propeller wash. That, in my opinion, would require icebreaker-level strengthening. Furthermore, when wind and currents create compression in the ice field, the escorted ships can fall behind and become completely immobilized. Ships have been sunk in such situations before the icebreaker managed to turn back and relieve the compression by breaking ice around the beset vessel.
Therefore, I would not take ice class 1C ship into anything but very marginal drift ice with such low concentration that there’s no chance it can turn into a high-concentration ice pack when the wind changes direction. I guess that would be okay around Greenland and Svalbard during the summer/autumn season as it’s mostly open water, but I would prefer a ship with a proper polar class. We once crossed a fjord in Svalbard with speedboats in thick fog, and suddenly there was a truck-sized iceberg which was so low that it would have not shown in the radar. Hitting that with a slightly older ship with poor watertight subdivision could even sink the vessel, as happened in Antarctica few years ago with MV Explorer…