Loosely based on Sergeant Murphy, the first American-bred horse, and the oldest (alongside Why Not in 1884) at age 13, to win the Grand National. The winning prize was £5,000. The horse was owned by John Sanford (1851-1939), an American businessman and breeder of thoroughbreds who also won the Kentucky Derby in 1916 and the American Grand National also in 1923, but with different horses each time. The real Sergeant Murphy had to be put down in 1926 after breaking a hind leg at a steeplechase race in Scotland.
James Cagney was offered the lead in the movie, but turned it down. It was then offered to Ronald Reagan, who was a reserve officer in the U.S. Cavalry at the time.
Col. Carruthers and later Pvt. Reilley are seen wearing the shoulder patch insignia of the U.S. Army's Second Cavalry Division. This unit was established on paper in 1921 but was not officially activated until 1940.