The Vikings invented the longboat during the Vikings Age from 800 to 1100 A.D. This type of ship helped them travel the oceans to reach France, England, Scotland, Greenland, Iceland, Ireland, Vinland and the Middle East. Thus, they became a dominant force in European medieval trade, politics and warfare.
The reason why the longboat was considered technologically advanced at the time is because of its capability to move by using the oars or a rectangular sail. Therefore, when there's no wind to blow the sail, the ship can still travel using the oars. The longboat, which had a shallow draft, was also built to traverse not just oceans but rivers as well. This allowed the Vikings to pass through the rivers of Eastern Europe all the way to the Middle East to trade.
The Vikings also utilized their expertise in studying the position of the North Star and the sun to help them navigate the seas. There are stories that tell about the sunstone, which is a navigating tool the Vikings used to tell the position of the sun even with dense clouds or fog. It is believed that the sunstones were crystals that served as natural polarizing filters to locate the sun's position. The sunstone has been regarded as a myth until recently when a possible sunstone was discovered from a 1592 ship that sank off Alderney, the northernmost Channel Island.