In 1840, San Jacinto was part of the Texas Navy flotilla led by Commodore Edwin Ward Moore which was dispatched to assist Yucatecan rebels that had taken up arms against Mexico.

They were identified as being "Purposely built and fitted out for use in the slave trade by the United States Consul General in Havana", and Viper was typical of the class.

[2] On 26 June 1840, the San Jacinto sailed from Galveston with instructions to blockade the Mexican port of Veracruz and seize enemy ships.

On 20 August, the San Jacinto rejoined Commodore Edwin W. Moore's flotilla and remained with them until being detached to Galveston with dispatches for the government.

A violent cold front approached but Lt. O'Shaunessy nevertheless went ashore, leaving Lt. Alfred G. Gray as senior officer on board.