Kennebec was launched 5 October 1861 by G. W. Lawrence, Thomaston, Maine; and commissioned at Boston Navy Yard 8 February 1862, Lieutenant John Henry Russell in command.

The new gunboat was assigned to Admiral David Farragut's newly created West Gulf Blockading Squadron and stood out to sea 12 February 1862.

Kennebec, in the gunboat division commanded by Captain Henry H. Bell, became entangled in the line of rafts which obstructed the river and struck one of the Confederate schooners.

As dawn had made their ships even more vulnerable targets, their commanders ordered the crews to lie flat on the decks while the gunboats drifted down stream out of action.

She remained below with Brooklyn continuing the shelling until Farragut had safely run by the Southern guns on the 28th and joined Flag Officer Charles Henry Davis above Vicksburg.

The tricky waters of the Mississippi ever threatened to fling the gunboat hard aground in hostile territory; and Confederate cannon and riflemen lay hidden ashore waiting to harass' the Union ships and their men.

On the last day of 1863, she made a prize of steamer Grey Jacket after the blockade runner had slipped out of Mobile laden with cotton, rosin, and turpentine for Havana.

Under the cover of darkness and the ready guns on board Metacomet and Kennebec, Watson led four boats directly to the grounded steamer and fired her in two places shortly after midnight 6 July.

By mid-morning all major Confederate opposition afloat had been destroyed or captured; and the rest of the day was spent rounding up Southern merchant ships.

After the war ended, Kennebec remained off the Texas coast providing stability as Union authority was restored and keeping an eye on events in Mexico, where French intervention had violated the Monroe Doctrine.