Collins's initial assignment was with the
8th Infantry Regiment at
Fort D. A. Russell, Wyoming. In March 1898, he was transferred to the
23rd Infantry Regiment at
Fort McIntosh, Texas, where he remained until June 1898. During the
Spanish–American War, he was assigned to 1st Brigade, 2nd Division,
Fifth Army Corps as
aide-de-camp to
William Ludlow and
Ordnance officer on the brigade staff. He took part in combat in Cuba, including the July 1898
Battle of El Caney and several subsequent skirmishes. After returning to the United States on sick leave in August, in December he rejoined the 23rd Infantry in Cuba as commander of its Company H. In March 1899, he was promoted to
first lieutenant and in April 1899, he transferred to the 8th Infantry. From May 1899 to January 1900, Collins performed recruiting duty in
Philadelphia. From January to July 1900, he was posted to Columbia Barracks near
Havana, where he served with the 8th Infantry during the
United States Military Government in Cuba. He served with his regiment at
Fort Snelling, Minnesota from July to September 1900, then departed for the
Philippines, where he took part in several skirmishes on
Luzon during the
Philippine–American War. From October 1900 to December 1901, he commanded Company E, 8th Infantry, and he was adjutant of the 8th Infantry's 2nd Battalion from June 1901 to May 1902. In May 1902, he was promoted to
captain in the
6th Infantry Regiment. After returning to the United States, Collins commanded the 6th Infantry's Company M at
Fort Leavenworth, Kansas. In May 1905, he was appointed regimental quartermaster and served again in the Philippines, this time at Camp Bumpus near
Tacloban. From March to October 1906, he was assigned to duty in
Zamboanga City. When he returned to the United States in late 1906, Collins was assigned to duty with the 6th Infantry at
Fort William Henry Harrison, Montana. ==Continued career==