Of such formidable dimensions were, according to Guiteras, the preparations made by Britain for the attack upon Havana. Little is heard of corresponding steps taken by her opponents. France was too exhausted to indulge in great expenditures of money or men. Spain was curiously unconcerned. The possibility of an attack upon Havana was discussed in Madrid, but the Spanish minister Grimaldi could not be made to believe that it might be successful. Cuba, too, little suspected what was in store for her. The new governor appointed to take the place of Cagigal, when the latter was promoted to the vice-regency of Mexico, was the Field Marshal D. Juan Prado y Portocasso. Before the consummation of the Family Pact, in March, 1670, King Carlos III. had told Prado of the menacing attitude of Britain and had warned him of the possibility of a rupture. He counted upon him to reorganize the island from a military point of view. Nevertheless Prado did not immediately after his appointment sail for Cuba, but lingered six more months in Spain, and, when he arrived on the island, wasted another month in a visit to his friend Madriaga, the governor of Santiago. He did not arrive in Havana until January, 1761. Valdes gives July as the month of his inauguration which seems improbable.
When Prado took charge of the governorship, he immediately proceeded to build quarters for the reenforcement of dragoons which were to be sent over from Spain, and for that purpose engaged sixty galley-slaves from Vera Cruz. He also began work on the fortifications of Cabanas under the direction of the excellent engineer Francois Ribaut de Tirgale. But a second consignment of galley-slaves in June brought to Havana the "vomito negro," the yellow fever, of which Siam had made a gift to Mexico in 1713 and which so far had been unknown in Cuba. Physicians being unfamiliar with the terrible scourge, all remedies proved of no avail. Within three months eighteen hundred men of the garrison and the fleet succumbed to the disease. The hospitals were filled with the sick, and work on the important public constructions was suspended. Engineer Tirgale was one of the first stricken. He was succeeded by his brother Balthazar, but he himself was sick and had such insufficient and inadequate help that he was much handicapped in his work. New difficulties having arisen with the vigueros, or tobacco-planters, Prado convoked the Junta which agreed to fix the process, the quantity and the brands of tobacco which the General Factory was to receive from the planters.