The earliest mention of Sitric in the Irish Annals is in 917 when he and Ragnall, another grandson of Ímar, are described as leading their fleets to Ireland. Sitric sailed his fleet to Cenn Fuait in Leinster, and Ragnall sailed his fleet to Waterford. Niall Glúndub, overking of the Northern Uí Néill, saw these Vikings as a threat, and he marched an army south to repel them. The Vikings fought against the men of the Uí Néill at Mag Femen in County Tipperary and claimed victory, though only through timely reinforcement by Ragnall and his army. This was followed by another at the Battle of Confey (also known as the Battle of Cenn Fuait), against Augaire mac Ailella, overking of Leinster, who died in the battle. Augaire's death marked the end of effective opposition to the Vikings' return to Ireland. Sitric led his men on a triumphant return to Dublin, where he established himself as king, while Ragnall returned to England and soon became King of Northumbria.