A Viking raid nearly always came as a total
surprise. The Vikings were expert
navigators and knew the coasts of Europe like the back of their hand.
They decided on a target and planned the attack in advance. Having the
fastest ships of the day they would arrive seemingly out of nowhere close
to the target and storm ashore ready to attack.
If needed, they could row their ships up rivers and if
the target was some distance from the river they would leave their ships,
round up available local horses and head for the church, convent or
village of their choice. They often had superior weapons and were well
trained, and usually got what they wanted. After the raid they would
return to their ships and sail away.
For the people attacked it was difficult to
organise a defence, because of the speed with which everything happened.
The effect on the people then would be be similar today to an attack by
troops brought in by helicopters to attack a peaceful small town.