The division's most famous combat operations were the Omaha Beach landings of June 6, 1944 (his 49th birthday), otherwise known as D-Day, and the taking of the French crossroads town of Saint-Lô in July 1944.

The younger Gerhardt attended the United States Military Academy (USMA) at West Point, New York, in 1913, where he earned a reputation as a skilled football, baseball and polo player.

In 1916, Gerhardt quarterbacked for West Point to a 30–10 upset win over Notre Dame, which was led by the famed freshman George Gipp.

[3] Among those he graduated alongside were men such as Matthew Ridgway, Mark W. Clark, J. Lawton Collins, Ernest N. Harmon, Norman Cota, William W. Eagles, Laurence B. Keiser, Frederick Augustus Irving, John T. Cole, Augustus M. Gurney, Elbert L. Ford, John M. Devine, Charles S. Kilburn, Harold R. Jackson, Basil H. Perry, Albert C. Smith, Clare Hibbs Armstrong, Daniel Noce, Aaron Bradshaw Jr. Harris M. Melasky, William C. McMahon and William Kelly Harrison, Jr., all of whom would, like Gerhardt, later become general officers, with Ridgway and Collins in particular becoming U.S. Army Chief of Staff.

[2][3] As part of the occupation force after the Armistice, Gerhardt played quarterback for the 89th Division squad that won the AEF football championship in March 1919.

In July 1943, taking over from Major General Leonard T. Gerow, he assumed command of the 29th Infantry Division, a National Guard formation which was then stationed in South West England in preparation for the Allied invasion of Normandy and had been there since October 1942.

[7] Major General Gerhardt was a hard taskmaster, a strict disciplinarian and considered by many of his men to be a martinet, who often became upset at small things such as a soldier not having the chinstrap of his helmet buckled.

He was also considered somewhat loose morally, as evidenced by a house of prostitution he established for his men near Rennes, France, which Lieutenant General Omar Bradley, the U.S. 12th Army Group commander, did not approve of and ordered closed.