While battles at sea were rare, they would occasionally occur when Viking ships attempted to board European merchant vessels in Scandinavian waters. When larger scale battles ensued, Viking crews would rope together all nearby ships and slowly proceed towards the enemy targets. While advancing, the warriors hurled spears, arrows, and other projectiles at the opponents. When the ships were sufficiently close, melee combat would ensue using axes, swords, and spears until the enemy ship could be easily boarded. The roping technique allowed Viking crews to remain strong in numbers and act as a unit, but this uniformity also created problems. A Viking ship in the line could not retreat or pursue hostiles without breaking the formation and cutting the ropes, which weakened the overall Viking fleet and was a burdensome task to perform in the heat of battle. In general, these tactics enabled Vikings to quickly destroy the meagre opposition posted during raids.