Arctic ice has melted to the second lowest level on record, with a million fewer square miles of sea frozen than in the 1980s and 1990s.

Stages, wharves and boats disappear during the tail ends of hurricanes or even squalls, but worse was the arctic ice that invade each spring.

Navigation beneath the arctic ice sheet was difficult.

For example, ice pieces flowing then jamming a spring river would be modeled very differently from a ship model traversing a simulated arctic ice sheet.

These ships, designed to be capable of independent operation in arctic ice conditions, were of extremely robust design and had strengthened hulls resembling those of polar icebreakers.