In 1796, when in command of the letter of marque schooner Favorite, of Martinique, he was very severely wounded and his ship was taken by a French privateer of very superior force after a fierce engagement of one hour and twenty minutes' duration.
In 1798 he was in command of the General Keppel, also of Martinique, which was capsized in a white squall on passage from Philadelphia, when Lennon and some of his crew were rescued by a passing schooner, after suffering great perils and hardships.
Unwilling to detain them further, Governor Maclean agreed to their sailing without convoy, on condition of Lennon hoisting his pennant as commodore.
Although harassed by Rossie, Commodore Joshua Barney, an American privateer of superior force, Lennon brought his vessels safe into the English Channel on 18 October 1812.
Two years later Lennon was attacked, on 19 July 1814, by the schooner Comet of Baltimore, U.S., an American privateer of sixteen guns and 136 men, which he beat off after a nine-hour fight, in which twelve out of his crew of twenty-two hands were killed or wounded.