In 1734 de Lezo was promoted by the king to Lieutenant General of the Navy.
He returned to South America with the ships Fuerte and Conquistador in 1737 as General Commander of the Spanish fleet stationed at Cartagena de Indias, in modern-day Colombia.
He took up his new post just prior to the conflict between Great Britain and Spain that would become known as the War of Jenkins' Ear and that would later be subsumed into the War of Austrian Succession.

In the early stages of the conflict, the British Admiral Edward Vernon undertook attacks on various Spanish outposts in America.
One such attack involved the capture of Portobelo (Panama), the dismantling of its fortifications and the subsequent withdrawal of British forces having left the place defenceless.

Admiral Vernon tested Cartagena de Indias on three separate occasions.
Both Vernon and Edward Trelawny, the British governor of Jamaica, considered the Spanish gold shipping port to be a prime objective.
The first attempt, in March 1740, was essentially a reconnaissance in force by a squadron including ships of the line, two fire ships, three bomb vessels, and transport ships.
Vernon's intention was to gather information on the city's topography and troop strength and to provoke a response that might give him a better idea of the defensive capabilities of the Spanish.

In May, Vernon returned to Cartagena de Indias in charge of 13 warships, with the intention of probing the city's defences.

The actual attack on Cartagena de Indias took place March 13 through May 20, 1741.
The British concentrated a fleet consisting of 196 ships, including 2,620 artillery pieces and more.
There were 10,000 soldiers, 12,600 sailors, 1,000 Jamaican slaves and 4,000 recruits from Virginia.
The defences of Cartagena de Indias comprised between 3,000 and 6,000 combatants, including regular troops, militia, and native archers, and six Spanish ships of the line and their crews.
Blas de Lezo's advantages consisted of a formidable primary fortress and numerous secondary fortifications.

On the evening of April 19, the British mounted an assault in force upon San Felipe.
Three columns of grenadiers supported by Jamaicans and several British companies moved under cover of darkness, with the aid of an intense naval bombardment.
The British fought their way to the base of the fort's ramparts but were unable to overcome de Lezo's defence.
They withdrew to Jamaica in late May with substantial casualties from both combat and disease.

Following the news of the disaster, Robert Walpole's government soon collapsed.
Spain retained control over its most strategically important colonies in the Americas, including the vitally crucial port of Cartagena de Indias that helped secure the defense of the Spanish Main and its trans-Atlantic trade with Spain.

News of Britain's defeat reached Europe at the end of June 1741 and had immense repercussions.
It caused George II of Great Britain, who had been acting as mediator between Frederick the Great of Prussia and Maria Theresa supporting Austria over Prussian seizure of Silesia in December 1740, to withdraw Britain's guarantees of armed support for the Pragmatic Sanction.
That encouraged France and Spain, the Bourbon allies, revealed to also be allied with Prussia, to move militarily against a now isolated Austria.
A war of wider scope, the War of the Austrian Succession, now began.
In 1734 de Lezo was promoted by the king to Lieutenant General of the Navy. He returned to South America with the ships Fuerte and Conquistador in 1737 as General Commander of the Spanish fleet stationed at Cartagena de Indias, in modern-day Colombia. He took up his new post just prior to the conflict between Great Britain and Spain that would become known as the War of Jenkins' Ear and that would later be subsumed into the War of Austrian Succession.
In the early stages of the conflict, the British Admiral Edward Vernon undertook attacks on various Spanish outposts in America. One such attack involved the capture of Portobelo (Panama), the dismantling of its fortifications and the subsequent withdrawal of British forces having left the place defenceless.
Admiral Vernon tested Cartagena de Indias on three separate occasions. Both Vernon and Edward Trelawny, the British governor of Jamaica, considered the Spanish gold shipping port to be a prime objective. The first attempt, in March 1740, was essentially a reconnaissance in force by a squadron including ships of the line, two fire ships, three bomb vessels, and transport ships. Vernon's intention was to gather information on the city's topography and troop strength and to provoke a response that might give him a better idea of the defensive capabilities of the Spanish.
In May, Vernon returned to Cartagena de Indias in charge of 13 warships, with the intention of probing the city's defences.
The actual attack on Cartagena de Indias took place March 13 through May 20, 1741. The British concentrated a fleet consisting of 196 ships, including 2,620 artillery pieces and more. There were 10,000 soldiers, 12,600 sailors, 1,000 Jamaican slaves and 4,000 recruits from Virginia. The defences of Cartagena de Indias comprised between 3,000 and 6,000 combatants, including regular troops, militia, and native archers, and six Spanish ships of the line and their crews. Blas de Lezo's advantages consisted of a formidable primary fortress and numerous secondary fortifications.
On the evening of April 19, the British mounted an assault in force upon San Felipe. Three columns of grenadiers supported by Jamaicans and several British companies moved under cover of darkness, with the aid of an intense naval bombardment. The British fought their way to the base of the fort's ramparts but were unable to overcome de Lezo's defence. They withdrew to Jamaica in late May with substantial casualties from both combat and disease.
Following the news of the disaster, Robert Walpole's government soon collapsed. Spain retained control over its most strategically important colonies in the Americas, including the vitally crucial port of Cartagena de Indias that helped secure the defense of the Spanish Main and its trans-Atlantic trade with Spain.
News of Britain's defeat reached Europe at the end of June 1741 and had immense repercussions. It caused George II of Great Britain, who had been acting as mediator between Frederick the Great of Prussia and Maria Theresa supporting Austria over Prussian seizure of Silesia in December 1740, to withdraw Britain's guarantees of armed support for the Pragmatic Sanction. That encouraged France and Spain, the Bourbon allies, revealed to also be allied with Prussia, to move militarily against a now isolated Austria. A war of wider scope, the War of the Austrian Succession, now began.
Blas de Lezo