Before involving his country in the conflict raging in Europe and across the world, Charles III of Spain made provisions to defend the Spanish colonies against the British Royal Navy. For the defence of Cuba, he appointed Juan de Prado as commander-in-chief.  De Prado arrived at Havana in February 1761 and began work to improve the fortifications of the city. In June 1761, a flotilla of seven ships of the line under the command of Admiral Gutierre de Hevia arrived at Havana, transporting two regular infantry regiments  totalling some 1,000 men. However, yellow fever quickly reduced the defending forces, and by the time of the siege, they had been reduced to 3,850 soldiers, 5,000 sailors and marines and 2,800 militia. The main garrison consisted of:. Did yellow fever strike troops before or after fortifications were made?