Meanwhile Cromwell had been wavering between a war against France or Spain. The need of a capture of money perhaps influenced him to turn against Spain, for this country still drew from her western colonies a tribute of gold and silver, which naturally would fall a prey to the power that controlled the sea. One month after Blake's exploit at Tunis, another English naval expedition set out to the West Indies to take Santo Domingo. Although Jamaica was seized and thereafter became an English possession, the expedition as a whole was a disgraceful failure, and the leaders, Penn and Venables, were promptly clapped by Cromwell into the Tower on their return. This stroke against Spain amounted to a declaration of war, and on Blake's return to England he was ordered to blockade Cadiz. One detachment of the plate fleet fell into the hands of his blockading ships and the silver ingots were dispatched to London. Blake continued his blockade in an open roadstead for six months, through autumn and winter, an unheard of thing in those days and exceedingly difficult. Blake was himself ill, his ships were not the copper-bottomed ones of a hundred years later, and there was not, as in later days, an English base at Gibraltar. But he never relaxed his vigilance. In April (1657) he learned that another large plate fleet had arrived at Santa Cruz, Teneriffe. Immediately he sailed thither to take or destroy it. If Porto Farina had been regarded as safe from naval attack, Santa Cruz was far more so. A deep harbor, with a narrow, funnel entrance, and backed by mountains, it is liable to dead calms or squally bursts of wind from the land. In addition to its natural defenses it was heavily fortified. Blake, however, reckoned on coming in with a flowing tide and a sea breeze that, as at Porto Farina, would blow his smoke upon the defenses. He rightly guessed that if he sailed close enough under the castles at the harbor entrance their guns could not be sufficiently depressed to hit his ships, and as he saw the galleons and their escorts lined up along the shore he perceived also that they were masking the fire of their own shore batteries. For the most difficult part of his undertaking, the exit from the harbor, he trusted to the ebbing tide with the chance of a shift in the wind in his favor.