During the English Civil War Penn, an experienced sailor, fought for Parliament and was appointed rear admiral of the Irish seas in 1647. He was arrested in 1648 on suspicion of corresponding with Charles I but was soon released. He fought in the First Anglo-Dutch War (165254) as vice admiral and then as general of the fleet. After secretly offering in 1654 to deliver the fleet to the exiled Charles II, he commanded the expedition sent by Oliver Cromwell to the West Indies, which captured Jamaica (May 1655) but failed to take Hispaniola. On his return he was briefly imprisoned, for reasons that are uncertain. Retiring to his estate in Munster in Ireland, he engaged in secret communication with the Royalists. At the Restoration (1660) he was knighted and appointed a commissioner for the navy. In the Second Dutch War (166567), he served as captain of the fleet with the Duke of York (afterward James II). Penn was the author of a code of naval tactics that was the basis of the Duke of Yorks Sailing and Fighting Instructions, long the orthodox tactical guide of the navy.

Given certain compositional changes and the distinctive style adopted this reduced version of Lelys imposing portrait is almost certainly that used as the basis for the engraving produced in 1833 by William Finden. Lelys portrait is one of the ‘flagmen’ portraits seen by Pepys on 18 April 1666 in Lely’s studio. It was listed as ‘to be done’, and was commissioned following the Battle of Lowestoft, the first fleet action of the Second Dutch War. The portrait was presented by George IV to Greenwich Hospital in 1824 and is now in the National Maritme Museum collection.