The final class of armored cruisers to be built for the US Navy, Montana and her sisters were armed with a main battery of four 10-inch (254 mm) guns, and they were capable of a top speed of 22 knots (41 km/h; 25 mph).

She made two cruises to the Mediterranean Sea to protect American citizens in the Ottoman Empire, the first in 1909 in the aftermath of the Young Turk Revolution and the second during the Balkan Wars in 1913.

Montana was also involved in political unrest in Central American countries, sending landing parties ashore in Haiti and in Mexico during the Occupation of Veracruz, both in 1914.

After the United States entered World War I in April 1917, Montana was tasked with convoy escort and training ship duties.

[1] The ship was propelled by two 4-cylinder, vertical triple-expansion engines, with steam provided by sixteen coal-fired Babcock & Wilcox water-tube boilers trunked into four funnels.

She had a storage capacity for up to 2,000 long tons (2,000 t) of coal, which allowed her to steam for 6,500 nautical miles (12,000 km; 7,500 mi) at a speed of 10 knots (19 km/h; 12 mph).

For defense against torpedo boats, she carried twenty-two 3-inch (76 mm) 50-caliber guns in single pedestal mounts either in casemates or sponsons in the hull.

After resuming her normal peacetime routine for the following three months, Montana was tasked with escorting President William Howard Taft aboard Tennessee for a trip to Panama.

On 26 July 1911, Montana was transferred to the Atlantic Reserve Fleet and she began an overhaul at the Portsmouth Navy Yard that lasted until 11 November 1912.

[12] After the United States entered World War I on 6 April 1917, Montana initially was tasked with transporting men and materiel in the York River area, along with conducting training exercises.

On 17 July, she was assigned to the Cruiser and Transport Force; she spent the majority of 1917 and 1918 escorting convoys from Hampton Roads, New York City, and Halifax, Nova Scotia to France.

[4] A troopship convoy followed in June 1918 in company with the cruisers South Dakota and Huntington and the destroyers Gregory and Fairfax, protecting the Italian steamers Re d'Italia, Caserta, and Duca d'Aosta, the French Patria, and American transports Pocahontas and Susquehanna.

[14] In September 1918, Montana took part in another troopship convoy to France with the battleship Georgia, the armored cruiser North Carolina, and the destroyer Rathburne.

[15] The convoy consisted of the transports Princess Matoika, President Grant, Mongolia, Rijndam, Wilhelmina, British steamer Ascanius.

During this period of inactivity, she was renamed Missoula on 7 June 1920 so her original name could be used for one of the planned South Dakota-class battleships, and she reclassified with the hull number CA-13.