After service in the Mediterranean, and time spent commanding his own ships, he was advanced to flag rank and joined the Royal fleets assembling for battle during the Second Anglo-Dutch War.

He benefited from his relationship to his brother, one of the closest friends of King Charles II and the Lord High Admiral, James, Duke of York.

Berkeley had commanded Bristol in Sir John's squadron in an attempt to persuade the Dey of Algiers, Ismail Pasha, to stop attacking English ships.

Reports of his actions during the battle were confused and contradictory, some accounts suggesting that he had taken a squadron of six ships and pursued nine Dutch vessels, others stating that he had abandoned the fight after the death of his brother, Charles.

[2][3][a] Poet Andrew Marvell added a critical verse suggesting the latter view was correct in his 1666 poem 'The Second Advice to a Painter': Berkeley had heard it soon, and thought not goodTo venture more of royal Harding's blood …With his whole squadron straight away he bore,And, like good boy, promised to fight no more.

[2]Berkeley was supported by the Duke of York, who appointed him Vice-admiral of the White, and William succeeded his dead brother as lieutenant-governor of Portsmouth later in 1665.

[4] He had by now been appointed vice-admiral of the blue and been given command of the van of the English fleet which sailed to engage the Dutch at the Four Days' Battle.

[1][6] His body was carried to Zeeland and embalmed by Frederik Ruysch, before being placed on public display, in a large sugar chest, in the Grote Kerk in The Hague for a time.

[2] Public opinion was that he had died gallantly, but Marvell presented an alternative viewpoint in 'The Third Advice to a Painter': And if the thing were true, yet paint it not,How Berkeley (as he long deserved) was shot,Though others that survey'd the corpse so clearSay he was only petrified with fear.