Sunflower was used as a gunboat by the Navy to patrol navigable waterways of the Confederacy in order to prevent the South from trading with other countries.

Sunflower—a screw gunboat purchased at Boston, Massachusetts, on 2 May 1863—was commissioned on 29 April 1863, Acting Master Edward Sice in command.

On Christmas Eve 1863, she captured blockade runner Hancock near the lighthouse at Tampa Bay with a cargo of salt and borax.

These Union ships transported Northern soldiers to Tampa and also provided naval landing parties which participated in the assault.

On the 6th, the three ships captured sloop Neptune which was carrying a cargo of cotton, when she attempted to run the blockade On 2 June, Sunflower landed three armed boats to destroy salt works at Tampa Bay.