After being installed with a large (13") mortar, Sarah Bruen was used by the Union Navy, in its blockade of Confederate States of America ports and waterways, as a gunship whose main task was to bombard elevated targets which could not be reached by standard cannon or rifled guns.

The mortar schooners shelled the Southern riverside forts for a week before Farragut's deep draft ships raced past the Confederate batteries and captured New Orleans, Louisiana.

The schooners sailed to the entrance to Mobile Bay which they blockaded until Flag Officer Farragut called them back to the Mississippi River to bombard new and increasingly strong Confederate batteries at Vicksburg.

They shelled the Southern emplacements at that river fortress during Farragut's dash past Vicksburg to meet Flag Officer Davis's Western Flotilla.

While Farragut was above the forts awaiting troops for a joint Army-Navy attack on Vicksburg, the collapse of General George B. McClellan's peninsula thrust toward Richmond caused the Secretary of the Navy to recall Porter and twelve of his schooners for duty supporting Union Army operations in the Richmond/Washington theater.