Siro was built by William Flanagan, reportedly at a cost of US$40,000,[4] and launched in 1812 at Baltimore for her owner George Stiles.

[3] In the autumn of 1812 she was sailing to France when she captured Loyal Sam, of ten guns, which was carrying specie worth US$23,500, and a cargo of indigo.

[b] Captain Thomas Mansell described Siro in a letter as being pierced for 16 guns though carrying twelve 9-pounders, and new and a fast sailer.

[14] On 21 September 1814 the USS Wasp was about 75 miles east of Madeira when she captured Atalanta, which was described as a British brig of eight guns and 19 men, carrying a commercial cargo.

[15] In his letter to the Secretary of War, Geisinger describes Atalanta as the former American schooner Siro, which Pelican had captured in the Bay of Biscay.

[17] The capture gave rise to a case before the Supreme Court of the United States over the status of a cargo owned by a neutral though carried in a vessel belonging to the enemy[12][13]