An ice-strengthened ship is a ship made of steel. These ships are built to navigate the Antarctic and Arctic ice. Today, most ships that cruise to Antarctica and the Arctic are ice-strengthened vessels. Hondius, Ortelius, and Plancius are all ice-strengthened ships. Both Ortelius and Hondius have the highest ice-class notation (UL1, equivalent to 1A-Super for Ortelius, and Polar Class 6, equivalent to 1A-Super for Hondius), making them suitable for navigation in medium first-year ice, which may include old ice inclusions. 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 fuel-intensive to run (sometimes powered by gas turbines or a nuclear generator). These ships, constructed for function, are uncomfortable to travel in on the open sea.