During subsequent service as a canal boat, the vessel caught the eye of the Federal Government which chartered her sometime in September 1858—quite possibly on the 13th of that month—for its forthcoming expedition to South American waters.

Their growing animosity prompted the dictator to turn against the continuation of surveying operations—which he had previously heartily endorsed—then being conducted in the tributaries of the Rio de la Plata by the American Navy's side-wheel steamer, USS Water Witch (1851).

The hostility reached a climax on 1 February 1855 when Paraguayan batteries at Itapiru—a brick fortress on the northern bank of the Upper Paraná River—opened fire upon that small American warship, hitting her 10 times and killing her helmsman.

Under the command of Lt. William Ronckendorff, M. W. Chapin – the smallest of the vessels and the last to reach the mouth of the Rio de la Plata – arrived at Montevideo, Uruguay, on 29 December.

A fortnight's negotiations—aided by the knowledge that the balance of Shubrick's force was nearby ready to launch offensive operations should such measures be needed—resolved the disputes to Bowlin's satisfaction, and the two American steamers headed downriver on 10 February.

Upon the successful completion of their mission to South America, the ships not assigned to the Brazil Squadron returned home where the Navy exercised its purchase option by buying all seven of the chartered steamers.

She was still serving there as a tender when the election of Abraham Lincoln to the Presidency on 6 November 1860 precipitated the secession crisis and set the United States on an inexorable course toward civil war.

But, in this instance, the withdrawal of cotton-belt states from the Union greatly intensified the customary disquiet and transmuted into it a deep and widespread anxiety concerning the safety of the city.

Washington's location on the river separating the Southern states of Maryland and Virginia prompted fears that Confederate sympathizers might attempt to prevent Lincoln's inauguration and try to take possession of the city.

Although the feared attacks did not occur when Lincoln took office, tension continued to grow in the weeks that followed; and the tempo of ominous events accelerated after the surrender of Fort Sumter.

Since she was larger, that screw sloop was capable of carrying more cargo than Anacostia; and, since her engines were far more powerful, she was better able to tow warships then under repair out of the threatened, and soon-to-be-abandoned, Norfolk Navy Yard.

In Baltimore, Maryland, on that same day, 19 April, a violently pro-Southern mob attacked the 6th Massachusetts Regiment as it was moving between railroad stations during its trip to Washington to defend the Federal Capital.

Since Fillebrown needed a pilot to descend the river below Cedar Point safely, he reversed course upon reaching that place, lest his ship run aground and fall into enemy hands.

Occasionally, she ventured all the way to Point Lookout, Maryland; but usually reversed course before reaching the mouth of the Potomac and steamed back to the navy yard where she replenished her bunkers with coal and quickly began another cycle.

During one of his ship's reconnaissance runs downriver in mid-May, Fillebrown learned from the side-wheeler Mount Vernon that Confederate forces had emplaced cannon at the mouth of Aquia Creek.

If he ordered Federal forces to attack the fortifications which were going up on the southern bank of the Potomac, he would assuredly offend many still loyal, but wavering, Virginians and would influence them to vote to withdraw from the Union in the forthcoming plebiscite on their state convention's ordinance of secession.

After losing this critical plebiscite, the Lincoln Government wasted no time in moving to check the growing threat to the National Capital from the south bank of the Potomac.

Moreover, it seems unlikely that Anacostia took part since she departed the Washington Navy Yard that morning and headed for the mouth of the Potomac to escort the steamer Sea Gull back to the capital.

"In the morning the Anacosta (sic) conveyed us to the Navy Yard at Washington – At Alexandria a large Secession flag floated over the City, and the wharves were lined with people, but there was no demonstration.

Anacostia met Thomas Freeborn, the flotilla's flagship, on the morning of 31 May, just as Ward was preparing to resume shelling the new Southern works at the mouth of Aquia Creek.

In compliance with Ward's orders, Anacostia and Resolute did not join in the cannonade, but remained just out of range of the Confederate artillery so that they would be ready to tow any of their consorts out of danger in the event one or both became disabled during the engagement.

A few days later, while she was inspecting shipping in the Potomac, the steamer received orders sending her to Fort Monroe to relieve the tug, USS Young America, which needed repairs.

The ships returned to that place on 9 March—the day of the historic battle at Hampton Roads between CSS Virginia, the raised and rebuilt Merrimack and USS Monitor—but found the Southern positions deserted.

Anacostia's next assignment took her back and forth between Washington and Hampton Roads on runs escorting Army transports carrying McCellan's troops to Fort Monroe for the impending campaign.

On the day Acting Master Nelson Provost, who had relieved Collins in command of Anacostia, reported the latter raid, Lee's army launched an offensive which routed Union troops in the Second Battle of Bull Run and seriously threatened Washington.

About a week later, the ship—accompanied by four other ships of the flotilla—returned to the Rappahannock River behind which Burnside, who had relieved McClellan in command of the Army of the Potomac, was assembling forces in a position to protect Washington while pushing toward Richmond.

On the afternoon of 4 December, Southern field artillery opened fire on Anacostia and three other Union ships, beginning a series of engagements which continued until Burnside's Army—which had crossed the Rappahannock on the 12th—was defeated in the Battle of Fredericksburg on the 13th.

For instance, acting on an intelligence report from the Army, parties from Anacostia and USS Currituck landed at Indian Creek, Virginia, on 3 April 1863 to find a large quantity of smuggled medical supplies.

Yet, Anacostia's labors, combined with the countless like efforts of her sister ships in the Union Navy to exact a growing and enervating toll on the South's steadily shrinking ability to fight.

However, the fear and tension following Lincoln's assassination in mid-April gave increased purpose and excitement to her last weeks of duty as her crew remained alert for any conspirators who might attempt to escape down or across the Potomac.