The greatest armed force that had yet been seen in West Indian waters had in the mean time sailed from England to join the expedition of Vernon. It consisted not only of British troops, but had been reenforced by recruits from the colonies north of Carolina. Its commander was Lord Cathcart, who, when they stopped to take on fresh water in Dominica, was taken violently ill with a malignant fever and succumbed. His death was a disastrous blow to the British, for it destroyed the unity of command which is indispensable for the success of military operations. Cathcart's successor was Wentworth, who not only lacked experience and firmness, but was a political opponent of the impulsive, irritable Vernon. Thus the enterprise seemed to be at the outset doomed to failure owing to the rivalry and the discord of the leaders. The fleet under their command consisted of twenty-nine line ships, eighty smaller vessels with a crew of fifteen thousand sailors and a land force of twelve thousand men. The expedition set sail from Jamaica without having agreed upon any definite plan of attack. Havana was the nearest point at which operations should be directed and besides her conquest would have given Great Britain supremacy over the Gulf. But Admiral Vernon saw everything only in the light of his own advantages and decided to go in search of the French and Spanish squadrons, without taking trouble to inform himself whether they had not already left. Finally a war council was held and it was decided to make an assault upon the tower of Cartagena. The squadron appeared before the city on the fourth of March and after a siege of twenty-two days succeeded in capturing the fort of Bocachica at the entrance of the harbor. Admiral Wentworth then made preparations to take the fort of San Lazare, which dominated the city. He planned to attack it with a force of two thousand men, but half of them, misunderstanding his directions, remained in camp. The squadron, too, failed to come to his assistance in time, and after a complete defeat he was forced to retire. Before the British had a chance to recover from the effects of this disaster, caused mainly by the lack of harmonious cooperation between their commanders, the rainy season set in. With it came the usual epidemic of tropical fever and alarmingly decimated the forces of the British. The blockade was for the time being abandoned and the survivors of the expedition returned to Jamaica.