On the ocean, therefore, the colonists were badly off, for Great Britain was here the worst enemy they could have. Her wooden walls had always been her chief reliance, and from the days when Drake and Howard and Raleigh defeated the Great Armada of Spain, they had asserted and maintained British supremacy at sea. During this long period of two hundred years the names of England's great naval captains had been a terror to all her enemies. There was Robert Blake, who beat off the Dutch, when Tromp sailed across the channel with a broom at his masthead as a sign that he would sweep the English from the seas. There were Sir Cloudesley Shovel and Sir George Rooke, who worsted the French in the great battle of Cape La Hogue; there was the doughty old Benbow, who, deserted by his captains, with his single ship kept at bay the squadron of M. Ducasse in the West Indies; there was Boscawen, who captured the fortress at Louisburg; Hawke and Anson, and finally Rodney and Howe, already famous, and destined to become yet more so in the war that was just begun. The fleets that these famous admirals led into action were composed of line-of-battle ships,--immense structures, with two, three, or even four gun-decks, some of them carrying as many as one hundred guns, and the smallest of them rated at sixty-four. After these came the frigates, which had only one gun-deck, but which carried a battery on the spar-deck also. These were not thought of sufficient strength to be really counted as a part of the fighting force, although the largest size, the 50-gun frigates, were sometimes taken into the line of battle. But generally they served as scouts or outposts for the great fleets, or they cruised by twos and threes in light squadrons, or even singly, to attack privateers or unarmed merchantmen, or to make a raid on unprotected coasts and seaports, or to carry orders to the different stations. For all these uses they were of great service, being generally faster than the line-of-battle ships, and yet carrying guns enough to make them formidable to all the lesser craft. After the frigates came the sloops-of-war, ship-sloops, and brig-sloops, as the English called them; not the little boats with one mast that we are accustomed to call sloops, but square-rigged vessels with three or two masts, as the case might be, and carrying twenty guns or so. With all these three classes of vessels the British were well supplied, and the larger ships carried what at that day were heavy guns, 18-pounders and 24-pounders. In 1775, when the war broke out, the Royal Navy numbered one hundred line-of-battle ships, one hundred and fifty frigates, and three hundred of the smaller vessels, and before the war ended it had two hundred and fifty thousand seamen in its service.