Over the years the 1640 naval battle of Paraíba (Brazil) has attracted the attention of several historians, including F.A. Varnhagen, H. Wätjen and J.C. Warnsinck, who made extensive use of Dutch sources. By combining the Dutch and Portuguese accounts, C.R. Boxer and, more recently, M.J. Guedes shed new light on the episode. The Portuguese material comprises the original papers of Fernando Mascarenhas, the commander in-chief of the armada. These papers are gathered in four voluminous codices and record events concerning the armada between April 1638 and October 1640. Written in Portuguese and Spanish, they comprise various documents, including correspondence, as well as instructions, reports, and minutes of meetings of the Council of Captains. The documents in these codices constitute the bedrock of this article which focuses on the armada leaders’ perceptions of their opponent during their sojourn in Brazil, a topic still insufficiently explored in the literature. Given the goal of the expedition, gathering information on the Dutch military and naval power was crucial for defining a strategy to oust them from Pernambuco. How did the armada leaders acquire intelligence? How reliable was it when cross-checked against other sources and to what extent did the outcome of the battle depend on it?