(Mon: t. 614; 1. 225'; b. 45'; dr. 6'6"; cpl. 69; a. 2
guns; cl. Casco)

The first Tunxis was launched on 4 June 1864 at Chester, Pa., by Reaney, Son, and Arnold; and commissioned at the Philadelphia Navy Yard on 12 July 1864.

On 21 September 1864, the light-draft monitor departed the sheltered waters of the navy yard on her maiden voyage. However, she soon began taking on water at such an alarming rate that she came about and returned to Philadelphia, where she was decommissioned later in the month.

On 19 October 1864. Tunxis entered William Cramp and Sons' Shipyard Philadelphia, for extensive refit and rebuilding. On i2 July 1866, two years to the day since her first commissioning, the monitor emerged from the complete overhaul far more seaworthy than before. Nevertheless, since her class design had proven disappointing, she was immediately laid up at League Island Navy Yard.

On 15 June 1869, her name was changed to Hydra; and, on 10 August, this ship was renamed Ostego. In 1874, Ostego was broken up for scrap, having never seen active service.