In 6mm Lee Navy caliber, the M1895 saw service with the United States Marines during the Spanish–American War, including the 1898 invasion of Guantanamo Bay, where a Marine battalion deployed four Colt guns (two of them borrowed from the USS "Texas"'s armory). The M1895 proved to be a significant advance in firepower for the Marines, who employed them in the first known use of machine guns by the American military to provide tactical support of infantry forces during an assault. In contrast, Army regular forces in the campaign were still burdened with heavy, manually operated Gatling guns that required heavy artillery carriages pulled by mule transport. Lt. Colonel Roosevelt's Rough Riders, a dismounted volunteer cavalry regiment that fought in Cuba, also deployed two M1895 Colt machine guns in 7×57mm Mauser caliber (built for export, both guns were privately purchased for the Rough Riders by family members of the troops), but although they did cause some Spanish casualties were reportedly somewhat unreliable. As Lt. Col. Roosevelt noted, "These Colt automatic guns were not, on the whole, very successful...they proved more delicate than the Gatlings, and very readily got out of order." The two M1895 guns were transferred to Lt. John Parker's Gatling Gun Detachment, who used them in the siege of Santiago.