In 1870, during his tour of duty on the steam sloop-of-war USS Mohican, Brownson and a detachment of men fought the Battle of Boca Teacapan against the pirate ship Forward in Mexican waters.

During the fighting, United States Marines and U.S. Navy sailors captured the enemy ship and defeated a superior force of pirates positioned at a shore battery.

After brief duty as executive officer of the steam frigate USS Powhatan, he was named Inspector of Hydrography for the Coast Survey.

Brownson was promoted to rear admiral in 1905, when he hoisted his flag on board the armored cruiser USS West Virginia as Commander, 4th Division, North Atlantic Fleet.

He served as Commander, Special Service Squadron in Central American waters and was Commander-in-Chief of the United States Asiatic Fleet from 15 October 1906 to 31 March 1907.