The "90-day gunboat" was launched by Larrabee & Allen of Bath, Maine, on 12 October 1861, and commissioned at Boston Navy Yard on 17 February 1862, with Lieutenant George Henry Preble in command.

Katahdin was assigned to the West Gulf Blockading Squadron to bolster its strength as Flag Officer David Farragut prepared for his epochal attack on New Orleans.

After passing the forts and sailing beyond the range of their artillery, the Union ships anchored opposite Quarantine abreast a Confederate encampment which raised a white flag.

The next morning Kineo and Katahdin guarded the right flank of the Union Army while Essex and Cayuga got underway to engage ironclad ram CSS Arkansas.

However, as the Union warships were closing on Arkansas, the ram's engines failed leaving her unable to flee or fight; she was set afire by her officers and abandoned before she blew up.

While the expedition was ashore, the gunboats protected them; and, shortly before the soldiers reembarked, naval gunfire beat back a Southern attack which threatened to cut off the landing party.

The value of this beef to the South can be attested by the fact that, four miles below Donaldsonville, about 3,000 infantrymen supported by nine field pieces struck back at the ships in a desperate attempt to recapture the cattle.

The troops and guns are concealed, and watch for us as we pass along and fire and flee.In January 1863 Katahdin was ordered to reinforce the blockade off Galveston, Texas after that port had been recaptured by the Confederacy on New Year's Day.

On 30 April 1864 she chased the former revenue cutter Harriet Lane and steamer Alice as they escaped from Galveston; but, after a brisk and lengthy race, Katahdin was finally outdistanced.