[4] After the conclusion of the Mexican War, Le Roy served aboard the frigate USS Savannah in the Pacific Squadron from 1849 to 1851.

He took part in the African Slave Trade Patrol as commanding officer of the steamer USS Mystic in the Africa Squadron in 1861.

She soon was in action, exchanging fire with Confederate artillery on Amelia Island on January 18, 1862, and capturing the schooner Mars on February 5, 1862.

She chased a steamer all day on June 24 without being able to capture her, but on August 22, 1862, she took the schooner Fanny and her cargo of salt off Charleston.

It returned fire, scoring hits on Keystone State, one of which struck her steam drum, rupturing it and scalding 20 men to death and injuring 20 others.

[5][6] After Keystone State decommissioned for an overhaul in the summer of 1863, Le Roy took command of the screw sloop-of-war USS Oneida in the West Gulf Blockading Squadron,[5] then moved on to command of the screw sloop-of-war USS Ossipee in the same squadron.

[5] Promoted to commodore on July 3, 1870,[2][5] Le Roy was on special duty at New London, Connecticut, during 1871 and was senior officer of the Board of Examiners from 1872 to 1873.

However, a month after he assumed command, unrest in Haiti threatened American interests there, and on March 14, 1876, the Department of the Navy directed Le Roy to send two ships to Port-au-Prince.

On April 1, 1876, the Department of the Navy ordered Le Roy to send a fifth ship – it suggested the new gunboat USS Huron – to visit ports on the east coast of Mexico.