He planned the medical details of the first American purpose-built hospital ship and was the first army surgeon in Alaska.

Two years after the birth of John, in 1850, their daughter Caroline Clay Hoff was born.

When the American Civil War erupted in 1861, Hoff volunteered for the U.S. Army and was assigned as surgeon, with the rank of major, to the 3rd New York Infantry Regiment.

He participated in the Battle of Big Bethel, where a lamp was shot out of his hands, and others in the Eastern Theater.

There he planned the medical details for the new ocean steamer J.K. Barnes, the first American purpose-built hospital ship.

Later he served in California and New York before joining the Army Medical Examination Board in Philadelphia 1874.