Roosevelt refers to a captured German military advisor as a "Hun." The derogatory epithet "Hun" for German soldiers was first used (by the German Kaiser Wilhelm II himself,) during the Chinese Boxer Rebellion of 1901 and did not become widely used until World War One, both well after the Spanish-American War.
When the captured machine gun is used by the rough riders to target San Juan Hill, Roosevelt orders them to "elevate 20 meters". Any US army commands given in 1898 would have been in feet, moreover the cowboys would have not known what 20 meters was.
In the final scene, Nash mentions not having visited his friends' graves since the "First World War". This term did not come into common usage until the Second World War. Before 1939, the 1914-1918 war was known as the Great War.
At the press conference while the Rough Riders are training in San Antonio, Roosevelt lists a sampling of the civilian occupations of the troopers and mentions "one man, whom I'm sorry to say, used to work for the Internal Revenue Service." In 1898 the agency was known as either the Bureau of Internal Revenue or the Federal Revenue Service, and Roosevelt's actual quote referred to "the Federal Revenue Service". The name Internal Revenue Service did not come into use until around 1918, and the three names were used interchangeably from 1918 until the name Internal Revenue Service became the sole official name in 1953.
After Roosevelt's first encounter with the Spanish, he is walking away from the battle scene getting an update on who was wounded and killed. During this scene, on the bottom left corner you can see a boom mic enter and leave the picture.
There are several mirror shots as the Spanish are preparing to defend against the American attack on San Juan and Kettle Hills. In particular, several Spanish soldiers are shown shooting Mausers that are suddenly left-handed, and two other Spaniards feed a Maxim machine gun from the left when the German later tells Roosevelt that the Maxim feeds from the right.
William Tiffany was not killed in action. He survived the Battle of San Juan Heights unhurt and was given a battlefield commission as a second lieutenant, but was among several Rough Riders who contracted and died of yellow fever while awaiting their return home after Spanish surrender.
John Hay was not in fact Secretary of State during the time of the Spanish-American War. William R. Day was in that position, Hay was the Ambassador to Great Britain and was appointed Secretary of State after the war had concluded.
At several points in the film, General Wheeler refers to Nathan Bedford Forrest, another Confederate cavalry general, as his "old friend" and quotes him approvingly. However, Wheeler and Forrest had a notoriously rocky relationship, stemming from the Kentucky Campaign when General Braxton Bragg transfered most of Forrest's troops to Wheeler's command. After a failed attack on Dover, Tennessee in February 1863, an enraged Forrest told Wheeler that "I will be in my coffin before I fight again under your command," leading ultimately to Forrest's transfer elsewhere. Wheeler may have grudgingly respected Forrest, but it's unlikely that he would have upheld him as the ideal cavalry officer given their antagonistic wartime relationship.
Roosevelt is shown in Cuba using a custom nickel-plated and engraved 1873 Peacemaker .44/40 revolver with ivory grips. In fact, Roosevelt carried a much smaller blued-steel .38 caliber Colt revolver, presented to him before departing the united states, by his brother-in-law, a navy officer. The revolver was salvaged from the sunken wreckage of the U.S.S.Maine, the battleship that blew up in Havana harbor under mysterious circumstances and propelled the Untied Staes into the war with Spain.
This revolver was on display in Sagamore Hill, Roosevelt's estate in Long Island, until being stolen in the late 1980s.
Many of the key real-life characters are depicted as members of "Troop G" under Capt. Buckey O'Neill. In reality, O'Neill Commanded Troop A, Hamilton Fish was a sergeant in Troop L, and Craig Wadsworth was in Troop K.
When training in San Antonio, Texas, the Rough Riders are shown drawing their equipment from the back of horse drawn wagons. In reality, their equipment was issued at The Quadrangle, a limestone structure that was the original army quartermaster depot in that city. The Quadrangle still stands on the post at Fort Sam Houston and serves as headquarters for the US Army North. Peacocks, rabbits and deer freely roam the grounds as they did in the 1800s.
Theodore Roosevelt had been an infantry company commander in the New York National Guard in the early 1880s; although he may have been out of practice in giving commands, he was no neophyte to the Army.
Although Frederick Funston did join and serve with the Cuban Revolutionary Army, it was two years earlier (1896) than depicted in the movie. He was given a leave of absence (due to malaria), and he returned to the U.S. before war was declared on Spain. Although he did serve in the Spanish-American War, it was not with the Cuban Revolutionary Army; it was with the U.S. Army. In May of 1898 he was commissioned a colonel in the 20th Kansas Volunteer Infantry and that regiment was deployed to Cuba.
In the film, Edward Marshall is seriously wounded by Spanish artillery fire during the Battle of San Juan Hill. In reality, Marshall was wounded by a Spanish sniper at Las Guasimas, the first battle depicted in the film.
General Wheeler did not have a son named William. Two of his sons served in the Spanish-American War: Joseph Jr., who served the fictional William's role as Wheeler's aide-de-camp, and Thomas, who drowned in an accident while serving on the USS Columbia.
Henry Nash is portrayed as a poorly educated stage robber. Although some sources indicate he may have once been a train robber named William Sterin, he was actually a school teacher before joining the Rough Riders and a graduate of DePauw University.