[1] Simpson was appointed midshipman in the United States Navy in February 1840, shortly before his sixteenth birthday.

He served afloat until late 1845, when he became a member of the first class of midshipmen to be trained at the new United States Naval Academy in Annapolis, Maryland.

[2] After graduation on July 9, 1846, Simpson reported to USS Vixen and participated in numerous bombardments during the Mexican–American War.

In 1883, he was appointed president of a board to select a site for a government gun factory and made another study trip to Europe.

[2] Rear Admiral Simpson died in Washington, D.C., December 1, 1888, and was buried in Cypress Hills Cemetery.