Felim O'Neill fought in the Ulster Army at the Battle of Scarrifholis in 1650 where it was routed by the Charles Coote. O'Neill escaped the battle and retreated with a rest of the Ulster army to the Charlemont Fort. Together with Lord Strabane, he held the fort against Coote inflicting heavy casualties on the English troops in the Siege of Charlemont but had to surrender on terms on 6 August 1650 and marching away with his remaining troops was expected to embark and take service in France. However O'Neill decided to rather go into hiding.