In 1739 he was a lieutenant of HMS Burford, Admiral Edward Vernon's flagship at the Battle of Porto Bello, and commanded the landing party which stormed the Castillo de Fierro.

In recompense for his brilliant conduct Vernon promoted him to the command of the fireship HMS Cumberland, in which he in 1741 took part in the Battle of Cartagena de Indias.

On 13 April, being then off Ushant, the Prince George caught fire, and out of a complement of nearly 800, some 250 only were saved; the Rear admiral himself was picked up, stark naked, by a merchant-ship's boat, after he had been swimming for about an hour.

When Boscawen returned to England, Brodrick blockaded the French ships at Cadiz so closely, that even the friendly Spaniards could not resist making them the subject of insolent ridicule.

The French ships did not stir out till the passage was cleared for them by a gale of wind, which compelled the blockading squadron to put into Gibraltar.