During her U.S. Navy service, Gettysburg operated with the North Atlantic Blockading Squadron, was involved in both the first and second attacks on Fort Fisher, helped lay telegraph cables between Key West, Florida, and Havana, Cuba, and undertook navigational surveys of the Caribbean Sea, the Atlantic Ocean, and the Mediterranean Sea.

[2] During sea trials, Douglas achieved 17.75 kn (20.43 mph; 32.87 km/h) and was declared the fastest channel steamer in existence at the time.

Designed to carry a mixture of passengers and cargo, Douglas was the first steam packet with a straight stern, no fiddle bow, and no figurehead.

Having made passage from the River Clyde in a time of 8 hours 30 minutes, her arrival off Onchan Head was heralded by cannon fire from the Conister Rock, Fort Anne, and the Castle Mona.

She attracted wide attention, and her speed made her a strong candidate for more advanced adventures and was acclaimed as "comme le premier" among cross-channel steamers.

While in the Isle of Man Steam Packet Company's colours, the only events of interest – apart from the way she broke the record for the home run – were two mishaps that occurred during her voyages.

The passenger, a sailor from the second rate ship-of-the-line HMS Majestic who had been home on leave from the Royal Navy, scaled his way up the foremast head whilst in a state of alcohol intoxication and got onto the forestay.

She subsequently was renamed Margaret and Jessie in honor of the daughters of her new owner, both of whom were on board her during her initial outbound blockade run from Charleston.

On 1 June 1863 off Nassau, however, Margaret and Jessie was fired upon and driven ashore by a United States Navy gunboat.

The U.S. Navy purchased Margaret and Jessie from the New York Prize Court for American Civil War service.

Gettysburg assisted with a devastating bombardment of Fort Fisher prior to amphibious landings by Union Army troops.

Though failing to take the sea face of Fort Fisher, the attack by the Navy and Marine Corps diverted enough of the defenders to make the Army assault successful.

Recommissioning on 3 December 1866, Gettysburg made a cruise to the Caribbean Sea, concluding it with her arrival at Washington, D.C., on 18 February 1867.

Gettysburg was laid up in ordinary until 6 November 1873, when she again commissioned at the Washington Navy Yard in Washington, D.C. She spent several months transporting men and supplies to the various navy yards on the United States East Coast, and on 25 February 1874 anchored in the harbor at Pensacola, Florida, to embark members of the survey team seeking routes for an inter-oceanic canal in Nicaragua.

Gettysburg transported the engineers to Aspinwall, Panama (then a part of Colombia), and Greytown, Nicaragua, and returned them to Norfolk on 10 May 1874.

After several more trips along the U.S. East Coast with passengers and supplies, the ship again decommissioned on 9 April 1875 at the Washington Navy Yard.

Recommissioned on 21 September 1875, Gettysburg departed Washington for Norfolk, where she arrived on 14 October 1875 and was assigned to assist in another of the U.S. Hydrographic Office expeditions to improve the safety of navigation.

According to various sources, she made a voyage to the eastern Atlantic Ocean, where her embarked Hydrographic Office team made use of the Thomson Sounding Machine to discover the Gorringe Ridge, a seamount about 130 miles (110 nmi; 210 km) west of Portugal along the Azores–Gibraltar Transform Fault, on 6 November 1875; they named it "Gorringe Bank" after Gettysburg′s commanding officer, Captain Henry Honychurch Gorringe, and spent time mapping it, determined that it contained two significant peaks, which they named Gettysburg — the highest, at depth of 20 meters (66 ft) — after the ship, and Ormonde, the second highest, at a depth of 33 meters (108 ft).

[12] The Dictionary of American Naval Fighting Ships, however, claims that Gettysburg did not depart Norfolk until 7 November 1875 and spent her cruise in the Caribbean, where she conducted hydrographic surveys in the West Indies that supported the creation of precise nautical charts.

During the next two years, she visited nearly every port in the Mediterranean, taking depth soundings and making observations on the southern coast of France, the entire coastline of Italy, and the Adriatic islands.

On 1 October 1878, while the ship was off the coast of Algeria, Landsman Walter Elmore rescued a fellow sailor from drowning, for which he was awarded the Medal of Honor.

[citation needed] Her iron plates corroded from years of almost uninterrupted service and her machinery weakened, Gettysburg was decommissioned on 6 May 1879.