Steel grinds against ice on the bow of Hungary's oldest icebreaker. The low engine rumble echoes through the hull.

Launched in 1959, Hungary's first icebreaker remains on duty. It pushes through thick sheets of ice as the region faces another freeze.

"It was the first of a series of icebreakers. Eight of these units were built in Hungary," says captain Peter Vaskovics as he pilots it along the Danube.

The Danube links 10 countries as it runs from Germany to the Black Sea. Nearly 100 million tons of goods move through its ports each year. Grain, fuel and metals depend on steady passage. The river supports billions of dollars in trade. It offers lower costs than road or rail.

But when winter grips Central Europe, the Danube can turn in days from a trade lifeline to a frigid barrier. 

"When the river is frozen over, it's impossible to sail in floating ice. There are certain ships that can still operate, but not many. And that’s sort of dangerous," Vaskovics says.

This winter, Arctic air drove temperatures near minus 20 degrees Celsius in parts of the region. Ice formed in harbors and bays. Slow sections froze first. Some upstream stretches closed as ice floes built up. That forced joint action along the river.

There are seven icebreakers in operation in Hungary. Each one is assigned a stretch of the Danube.

Icebreakers' hulls are reinforced. They ride onto the ice and crush it with weight, not speed. In harsh winters, ships work in pairs: One breaks the surface, the other pushes floes downstream. That helps prevent blockages near ports and bridges.

"The technique is that you always start breaking ice from downstream and against the current, because once that area is frozen over, then broken," explains Vaskovics. "Then it means the ice floes go behind, downstream. If you started from above, then the ice will be just stuck."

This season, ice floes closed parts of the river in Slovakia. Commercial traffic slowed for a time. Crews across borders moved to reopen channels.

In Hungary, Icebreaker One returned to duty – another winter added to its record. An old ship, built for this task and still fit for it, keeping a vital trade route open when the river turns hard as stone.