Actually during that time frame there is no record of what we term and understand as 'Vikings' anywhere near Britain.
That comes later after 700AD. What their ancestors were doing.. from the departure of the Romans from Britian as we have it recorded... was essentially fighting amongst themeselves throughout Scandanavia.
But you pose an interesting question reference the Roman fleet. By the departure.. it would have been essentially a Romano-British fleet and it's quite possible they were as much pirates as traders. Especially those who remained in the region.
Because one thing is for sure... the later Vikings... were not the only ethnic group operating in either the North Sea or English channel. The Frisians, Batavians and early Angles andSaxons spring to mind as well.
Then of course on the other side of the Island you got them pesky Irish..Scots (Picts before them) and Welsh who seemed to enjoy raiding as much as any.
Edited by Centrix Vigilis - 03-Oct-2011 at 03:37