An ice-strengthened ship is a ship made of steel. These ships are made to get through the ice at Antarctica and the Arctic. Nowadays, most of the ships that cruise to Antarctica and the Arctic are ice-strengthened ships. Ortelius and Plancius are both are ice-strengthened ships. Ortelius has the highest ice-class notation (UL1 equivalent to 1A) and is therefore very suitable to navigate in solid one-year sea ice and loose multi-year pack ice. Plancius has an ice-class notation of 1D.
Icebreakers are needed if there is a trade route to keep ice free, if there are military reasons for patrolling in areas with heavy sea ice or if you need to work in heavy ice conditions, particularly in winter. Icebreakers are expensive to build and very expensive in fuel to run (sometimes powered by gas turbines or a nuclear generator). They are uncomfortable to travel in on the open sea.