In February, 1648-9, he was made a commissioner of the navy, and appointed to serve on that element, for which he seems by nature to have been designed.  He was soon afterwards sent in pursuit of prince Rupert, whom he shut up in the harbour of Kinsale, in Ireland, for several months, till want of provisions, and despair of relief, excited the prince to make a daring effort for his escape, by forcing through the parliament’s fleet:  this design he executed with his usual intrepidity, and succeeded in it, though with the loss of three ships.  He was pursued by Blake to the coast of Portugal, where he was received into the Tagus, and treated with great distinction by the Portuguese.

Blake, coming to the mouth of that river, sent to the king a messenger, to inform him, that the fleet, in his port, belonging to the publick enemies of the commonwealth of England, he demanded leave to fall upon it.  This being refused, though the refusal was in very soft terms, and accompanied with declarations of esteem, and a present of provisions, so exasperated the admiral, that, without any hesitation, he fell upon the Portuguese fleet, then returning from Brasil, of which he took seventeen ships, and burnt three.  It was to no purpose that the king of Portugal, alarmed at so unexpected a destruction, ordered prince Rupert to attack him, and retake the Brasil ships.  Blake carried home his prizes without molestation, the prince not having force enough to pursue him, and well pleased with the opportunity of quitting a port, where he could no longer be protected.

Blake soon supplied his fleet with provision, and received orders to make reprisals upon the French, who had suffered their privateers to molest the English trade; an injury which, in those days, was always immediately resented, and if not repaired, certainly punished.  Sailing with this commission, he took in his way a French man of war, valued at a million.  How this ship happened to be so rich, we are not informed; but as it was a cruiser, it is probable the rich lading was the accumulated plunder of many prizes.  Then following the unfortunate Rupert, whose fleet, by storms and battles, was now reduced to five ships, into Carthagena, he demanded leave of the Spanish governour to attack him in the harbour, but received the same answer which had been returned before by the Portuguese:  “That they had a right to protect all ships that came into their dominions; that, if the admiral were forced in thither, he should find the same security; and that he required him not to violate the peace of a neutral port.”  Blake withdrew, upon this answer, into the Mediterranean; and Rupert, then leaving Carthagena, entered the port of Malaga, where he burnt and sunk several English merchant ships.  Blake, judging this to be an infringement of the neutrality professed by the Spaniards, now made no scruple to fall upon Rupert’s fleet in the harbour of Malaga, and, having destroyed three of his ships, obliged him to quit the sea, and take sanctuary at the Spanish court.