These dramatic events were the subject of the first instalment of Kitson's two-volume life, subtitled "Portrait of a Soldier" and published in 1994. A distinguished soldier and an expert in low-intensity warfare, the author is particularly well qualified to assess Rupert's merits as a field commander. This concluding volume, however, deals with Rupert's lesser-known achievements at sea.
The son of the Protestant Elector Palatine and Princess Elizabeth, the beautiful daughter of James I, Rupert was less than a year old when his parents - recently crowned King and Queen of Bohemia - were driven from Prague in 1620 by the troops of the Catholic League. Most of his youth was spent in exile in the United Provinces (now Holland); in 1648 - when this story begins - he returned there to take command of the small Royalist fleet on behalf of his cousin, the Prince of Wales (soon to become Charles II on the execution of his father).
Over the next four and a half years, despite a constant rate of attrition from sea battles and storms, Rupert kept the Royalist navy afloat by sheer bloodyminded determination. On one occasion, he used his imposing physique (he was 6ft 4ins tall) to stifle an incipient mutiny by holding the ringleader over the side of his ship, hauling him to safety only when the crew agreed to obey orders.
Kitson is of the opinion that Rupert quickly "grasped the connection between seamanship and tactics that was indispensable to operational success at sea". However this knowledge did not prevent him from making amateurish mistakes. Like when, in the autumn of 1650, he ignored the warning signs and allowed a fleet of the new English Republic - known as the Commonwealth - to sneak up on his own divided force in the Mediterranean. He escaped with just two ships.
Nor had his epic voyage achieved much by the time he anchored his one remaining ship and four prizes off St Nazaire in the spring of 1653. "It did not," admits Kitson, "influence the outcome of operations in Ireland or succeed in sinking or capturing any Commonwealth warships ... Equally, it failed to coordinate or prolong the defence of Royalist interests in the West Indies." On the other hand, Rupert did manage to capture a number of prizes, and some of the proceeds were used to sustain the Royalist cause elsewhere.
With the Restoration of Charles II in 1660, Rupert returned to England and a pension of pounds 4,000 a year. Five years later, as trading disputes resulted in war with the United Provinces (the second Dutch War), he was made Admiral of the White and played a prominent part in the great naval victory over the Dutch, known as the Battle of Lowestoft that summer. But his finest moment came in July the following year, at the St James's Day Battle, when his novel tactics put a superior Dutch force to flight, inflicting 7,000 casualties in the process (the English lost just 1,200).
Kitson's conclusion is that had Rupert been killed in this battle, like Nelson was at Trafalgar, "he would probably have been remembered as one of the greatest of England's fighting admirals". Instead he survived to command the fleet again in 1673 (during the third Dutch War), and fought out a disappointing draw at the Battle of the Texel.
There is no doubt that Rupert was almost as daring on the high seas as he had been in the saddle: his breaking of the Dutch line from the leeward position during the Four Days' Battle in June 1666 has been acclaimed as an innovative manoeuvre of genius. But to compare - even obliquely - his victory in the St James's Day Battle to Nelson's at Trafalgar is probably a little extravagant. In the former engagement the enemy lost just two ships, though many were badly damaged; in the latter, 18 were captured or sunk. Furthermore, Rupert's victory was due in part to the fleet's joint commander, the Duke of Albemarle.
Kitson admits that he has not "unearthed any startling new material", which is hardly surprising given that he seems to have relied solely on printed sources. Nevertheless, his description of naval warfare in the 17th century is fascinating, though a somewhat dry text could have benefited from more direct quotation, not least of the subject himself. We are left with an intriguing portrait of Rupert the Admiral; but of Rupert the Man there is less evidence.