The Parliamentary garrison on the Isles of Scilly defected to the Royalists in 1648. The islands became a base for Royalists until Parliamentary admiral Robert Blake subdued them in June 1651. The militia on the Isle of Man mutinied against the Royalist Countess of Derby in 1651; with reinforcements from Robert Duckenfield, the island came under Parliamentary control in October. In Guernsey the population was Parliamentarian, but Governor Peter Osbourne and his Royalist troops had occupied Castle Cornet in 1643 and constantly exchanged fire with the town of St. Peter Port for almost nine years. In 1651, Admiral Blake blocked Royalist supply ships from Jersey and the garrison surrendered on 9 December. The island of Jersey surrendered to Parliament on 12 December 1651, after the fall of Elizabeth Castle to Blake.