Castledore was ordered by the United Merchants' Shipping Company of London and built by William Gray & Co. at West Hartlepool in 1956. Registered at 7,952 tons gross (4,581 net and 11,441 deadweight), she measured 456 feet in length with a 60 foot beam, and was constructed with seven riveted and welded bulkheads. A two-decked closed shelter deck ship, she had five holds reached from six hatchways and her cargo was handled by ten winches and four derricks. Engined by the Central Marine Engineering Works, her triple-expansion 3-cylinder engines could produce 3,700ihp. and she could steam at 12½ knots.