[1] His early service was in frigates Congress and United States, and during the Mexican–American War he took part in the attack on Alvarado, the capture of Tobasco, and the bombardment of Vera Cruz.

[2] During the early months of the Civil War, Jeffers commanded Philadelphia in the Potomac River and served in frigate Roanoke off Charleston and Hatteras Inlet.

In December 1861 he took command of Underwriter and soon afterward took part in the capture of Roanoke Island and the destruction of the Confederate squadron at Elizabeth City.

After the wounding of Captain John Lorimer Worden of USS Monitor during her historic engagement with CSS Virginia on March 9, 1862, Jeffers assumed command,[3] taking part mainly in shore bombardment in the James River.

Commodore Jeffers served in thar capacity for eight years and contributed much to the science and literature of naval ordnance.