Raguaillo d'Oceano is a masque composed in 1640 by Mildmay Fane, second Earl of Westmorland, for the entertainment of his own household and friends at his Northamptonshire mansion. It presents in allegorical terms a voyage of discovery: all the peoples from the four continents ask King Oceanus leave to conquer the still-unexplored, fifth corner of the globe, Terra Australis Incognita. Their flashy garments adorned with Latin inscriptions warn against a spiritual and historical disgrace and greed ruling over humankind in spite of geographical boundaries. Raguaillo d'Oceano reveals the official and personal views, on the topical issue of sea voyages, of a Royalist and Puritan land-owning aristocrat with a passion for the sea. The masque voices Fane's criticism of contemporary England's encouragement of state-funded maritime voyages, both from a political and moral point of view, an opinion which is however reconciled with the author's interest in things maritime, from geography to contemporary expeditions, and from navigation to constellations. This essay presents a case-study on the unexpectedly complex cultural history of Raguaillo d'Oceano, as a key to unlock an aristocrat's views on England's increasing attention to its developing overseas commerce and plans for maritime conquest in the 1630s and 1640s.