Rachel Seaman was armed as a gunboat and assigned to the Union blockade of the ports and waterways of the Confederate States of America.

On 6 October, Rachel Seaman captured British schooner Dart attempting to run the blockade at Sabine Pass.

On 15 October boat crews from Rachel Seaman and Kensington destroyed a railroad bridge at Taylor's Bayou, Texas, preventing Confederate reinforcement of Sabine Pass with heavy guns.

Almost a year later, while sailing north, on 13 April 1864, she captured her last prize British schooner Maria Alfred off Mermentau River, Louisiana.

The schooner arrived at New York City 21 May and for the remainder of the Civil War served as a supply ship along the Atlantic coast.