Emma Henry, an iron-hulled sidewheel steamer, was captured at sea in December 1864 attempting to run the Union blockade of the Confederacy.

At Norfolk, Virginia, Emma Henry joined the squadron commanded by Acting Rear Admiral Sylvanus W. Godon, which had been established to search for the Confederate ironclad ram CSS Stonewall.

The original reason for the squadron's dispatch, Stonewall, had long since ceased to pose a problem; the former Confederate ironclad had surrendered to Spanish authorities in Cuba on 19 May just as Wasp had begun her repairs at Philadelphia.

The war lasted until mid-1870, peace coming only after the complete reduction of Paraguay and the death of Lopez at the hands of Brazilian lancers following a protracted guerrilla campaign.

After the war ended in June 1870, Wasp continued to operate out of Montevideo in Uruguay on the aforementioned rivers, ascending them as far as Asunción, Paraguay.