I did not know that yesterday!

The Christian Science Monitor likens an icebreaker ship to a blocker on a football team -- the icebreaker plows through the defense to get the ship where it needs to go. But these ships don't use sheer force alone. A specially shaped hull, extra-strong steel plating, and powerful engines all work together to help ships break through thick Arctic and Antarctic ice.

Early icebreaker ships were made of wood, and the hull often had a rounded bow. These ships rammed into ice and tried to break it by brute force. Wood has some flexibility and resiliency, which helped the ships withstand some of the pressure of the ice. But the older shape and materials had their limits.

Modern icebreakers have a stepped hull designed to help the ship rise up on top of the ice and then crush downward through it. This allows the weight of the ship to break the ice like a giant sledgehammer. The hull is made of thick steel that has good low-temperature strength. Inside the hull is a massive support structure with closely spaced steel ribs. The thickness of the steel and the structure keep the ship from breaking under pressure.

The ship's powerful engines propel the hull up and forward, then gravity does the hard work of breaking thick polar ice. As many as six diesel-powered generators may be needed to run an icebreaker, and some ships are even nuclear-powered.

Source: ask.yahoo.com