The wound in his arm proved to be so serious that amputation was found to be necessary in order to save his life. General Shields, who was present at the operation, was affected even to tears at the fortitude displayed by Sweeny, who, notwithstanding the fact that no anæsthetics were used, showed not the slightest signs of flinching under the terrible ordeal. On his return to New York city, in 1848, Lieutenant Sweeny was received with much honor; he was brevetted captain by the governor of the state, and was presented a silver medal by the city government. He was also given a “grand reception ball” at Castle Garden, which was described as the “largest and most brilliant ball of the season.” Among the invited guests were ex-President Martin Van Buren, Major-Gen. John A. Quitman, U. S. A., Hon. Simon Cameron of Pennsylvania, Hon. William B. Maclay, M. C., representatives of the city and state governments and other people of note. On recommendation of General Scott, Sweeny was appointed by the president a second lieutenant in the Second United States Infantry, March 3, 1848, and from March to July, 1848, he was stationed at Fort Columbus, Governor’s Island, New York harbor. During August and September, 1848, Lieutenant Sweeny was at Jefferson Barracks, Missouri, and in October, 1848, he was stationed at Fort Hamilton, New York harbor, on recruiting service. Nov. 8, 1848, his regiment, under command of Brevet Maj.-Gen. Bennett Riley, who had been appointed military governor of California, sailed from New York for California _via_ Cape Horn. At Rio Janerio, where they stopped several days, they were entertained at a ball aboard the United States steamship _Brandywine_. They reached Monterey, Cal., April 6, 1849, and soon established regimental headquarters at San Diego. On June 11, 1851, Sweeny was promoted to be first lieutenant in the Second Infantry. In 1852 he engaged in the Yuma Indian War, and commanded an expedition of twenty-seven men, who penetrated into the Cocopa country in May, and after a sharp engagement, captured one hundred and twenty-five armed warriors and marched them into Camp Yuma, where a treaty was entered into which broke up the confederation of the River tribes. While engaged on this duty, Sweeny received a severe arrow wound in the neck. In 1854 he was ordered to Fort Pierre, in what was then northern Nebraska, where he served as aid to Gen. William S. Harney, participating in the campaign against the Sioux in 1855–’56, and was present at the “Great Treaty” made with the Sioux nation at Fort Pierre, at which many famous chiefs were present. In 1858 Sweeny was ordered to New York city on recruiting service, and was stationed there when the Rebellion broke out.