855 - Bjorn Ironside arrived in France

Claus Deleuran: Viking retreat
France
A Viking army sailed up the Seine to Pîtres (18 July). He was joined on August 17 by Bjorn Ironside. They looted the Perche region before the Loire Vikings were attacked by a Viking chieftain called Sigtrygg (Sidroc). Sigtrygg had been operating around the Seine and in Ireland, and had in the past sailed with Gudrød. He was now allied with Erispoë, who had paid him to get rid of Hallstein, Gudrød and Åsgeir And defeated them at Saltus articus
The viking army, which had suffered heavy losses in the Loire area, where only 300 vikings survived made a winter camp at a French island in the river, named Jeufosse.
Orkney Islands
Ketil Flatnose attacks the restt of the Pictish kingdom of Dalriada
Orm, Viking raider
Ireland
Cerball mac Dunlainge slaughtered a bunch of Viking intruders, led by Rodolb. In the aftermath of the battle Cerball mac Dunlainge was captured by Vikings, but he escaped.

Cerball joined a group of Danes led by a chief named Orm in their war with the Norwegians. These Danes might have come from Waterford. People of  Munster begged for Cerball's help against the Vikings, and Cerball with local Irish from Osraige & Munster  And Orm's Danish vikings inflicted a heavy defeat on the Norwegians.
Wales 
Dubh-Ghenti led by a Norse-Irish chieftain named Orm attacked Gwynedd, only to be repelled by Rhodri Mawr who killed Orm.