He was the second of three sons born to Edward Roddam, and his wife Jane.[1] Roddam entered the navy in 1735, joining the 20-gun HMS Lowestoffe as a midshipman under Captain Drummond, with whom he served in the West Indies for the next five years.[1][2] He then transferred in succession to the 80-gun ships HMS Russell, HMS Cumberland and HMS Boyne. During this time he served with Sir Chaloner Ogle and Sir Edward Vernon at the Battle of Cartagena de Indias, and the occupation of Cumberland Bay in 1741.[1][2] He distinguished himself during these encounters, and narrowly escaped being killed, when a cannonball shot off part of his coat.[2] He was promoted to third lieutenant of the 60-gun HMS Superb on 2 November 1741, and served under her commander, Captain William Hervey.[1][2] Roddam was present when Superb encountered a Spanish ship off the Irish coast during her voyage back to Britain. The Spanish ship, measuring 400 tons, was armed with 20 guns and manned by a crew of 60, was captured, and later valued at £200,000.[3]