The war at sea which followed was a war of giants. No such mighty fleets have ever disputed the sovereignty of the seas, nor have any naval battles equalled the encounters of the two nations in dogged and obstinate fighting. In the spring of 1665 the two fleets, each a hundred ships strong, mustered in the Channel, the Dutch under Opdam, the English under the Duke of York. Their first battle off Lowestoft, obstinate as all the engagements between the two nations, ended in a victory for the English, a victory due chiefly to the superiority of their guns and to a shot which blew up the flag-ship of the Dutch Admiral in the midst of the engagement. But the thought of triumph was soon forgotten in a terrible calamity which now fell on London. In six months a hundred thousand Londoners died of the Plague which broke out in May in the crowded streets of the capital, and which drove the Parliament from London to assemble in October at Oxford. To the dismay caused by the Plague was added the growing irritation at the increasing pressure of the war and a sense of the grave dangers into which the struggle with Holland was plunging the country both at home and abroad. The enormous grant which had been made at the outset for three years was already spent and a fresh supply had to be granted. But hard and costly as the Dutch war had proved, a far graver and costlier struggle seemed opening in its train. The war was a serious stumbling-block in the way of the French projects. Holland on the strength of old treaties, England on the strength of her new friendship, alike called on Lewis for aid; but to give aid to either was to run the risk of throwing the other on the aid of the House of Austria, and of building up the league which could alone check France in its designs upon Spain. Only peace could keep the European states disunited, and it was on their disunion that Lewis counted for success in his design of seizing Flanders, a design which was now all but ripe for execution. At the outset of the war therefore he offered his mediation, and suggested the terms of a compromise. But his attempt was fruitless, and the defeat off Lowestoft forced him to more effective action. He declared himself forced to give aid to the Dutch though he cautiously restricted his help to the promise of a naval reinforcement. But the chief work of his negotiators was to prevent any extension of the struggle. Sweden and Brandenburg, from both of which powers Charles counted on support, were held in check by the intervention of France; and the Bishop of Münster, whom an English subsidy had roused to an attack on his Dutch neighbours, was forced by the influence of Lewis to withdraw his troops. Sir William Temple, the English ambassador at Brussels, strove to enlist Spain on the side of England by promising to bring about a treaty between that country and Portugal which would free its hands for an attack on Lewis, and so anticipate his plans for an attack under more favourable circumstances on herself. But Lewis knew how to play on the Catholic bigotry of Spain, and the English offers were set aside.