During the Confederate Wars set off by the Irish Rebellion of 1641, Lord Forbes, commanding forces of the English Long Parliament, was allowed by the then Lord Barnabas O'Brien to occupy Bunratty in 1646. Barnabas did not want to commit to either side in the struggle, playing off royalists, rebels and roundheads against each other. He left for England, where he joined King Charles. Defence of the castle, whose position allowed those holding it to blockade maritime access to Limerick (held by the Confederates) and the river Shannon, was in the hands of Rear-Admiral Penn, the father of William Penn, founder of Pennsylvania. After a long siege, the Confederates took the castle. Penn surrendered but was allowed to sail away to Kinsale.