The first Viking raids were not led by their kings. Some guess there was a lack of food. The first raids were not about settling and taking over a new land. They looted and they returned home.
Later, raids were led by kings and they did settle in areas they conquered.
You can see in this photo their long swords. They also had long axes. They had wooden shields. They did not have full body armor. And they did not have horns on their helmets.
One famous kind of Viking warrior was the berserker. He went without armor. He’d dress in animal skins. We have an expression, “to go berserk.” It means to scream and go crazy. That’s what they did. They screamed and ran into battle without armor. They believed the god of war would protect them.
Raiding groups were not big. Small groups could easily sneak up on coasts, sail up rivers, go onto land, and could easy attack places like unprotected monasteries.
When the Vikings invaded Britain, they brought 300 ships and about 6000 men, which was a huge army for that time.
You can see their ships were ideal for narrow waterways, shallow waterways, as well as longer voyages across the sea. Their longboats allowed them to use their sails in the open waters and use oars when needed. They could also travel forward and backward. They were highly maneuverable, which made them great for warfare.
Pictures are from public domain sources.