[4] After the collapse of the revolution, he was forced to leave the country for his own safety and fled to the United States via Switzerland,[3] arriving in America in 1850.

[5] Gerhardt was politically active and favored the nascent Republican movement, although he largely hid these affinities due to their controversial nature.

Anticipating the outbreak of war, Gerhardt helped organize a 65-member company of volunteer infantry known as the "Turner Rifles" on January 11, 1861.

[11] He accompanied the regiment to its temporary station at Annapolis, Maryland, and then in November to its staging area at Hilton Head, South Carolina.

[12] The unit returned to the Union base at Newport News, Virginia, in July 1862, where it was assigned to the newly formed IX Corps.

[12] His unit played a role in helping to stabilize the Union line at Fox's Gap during the Battle of South Mountain on September 14, 1862, near Boonsboro, Maryland.

[13][14] His unit came under friendly fire by the 9th New Hampshire Volunteer Infantry before reaching the line of combat, and his soldiers only saved themselves by throwing themselves down on the ground.

Gerhardt commanded the 46th New York Volunteers as it participated in the Siege of Vicksburg (then nearing its conclusion), and in the Jackson Expedition.

[11][18] Gerhardt returned to live in the District of Columbia after the war, where he established a restaurant[9][19] and remained active in local Republican Party politics[20] as well as German community groups (such as the Washington Schuetzen Verein).

[24][25] He was buried at Prospect Hill Cemetery in Washington, D.C.,[25] and the artillery unit of the District of Columbia militia fired an 11-gun salute over his grave.