Tuscaloosa devoted the autumn to a shakedown cruise which took her to Rio de Janeiro, Buenos Aires, and Montevideo, before she returned to the New York Navy Yard shortly before Christmas.

After a stop at Guantánamo Bay, Cuba, she transited the Panama Canal on 7–8 April and then steamed north to San Diego, where she joined Cruiser Division 6 (CruDiv 6) in time to participate in Fleet Problem XVI staged in May in the northern Pacific off the coast of Alaska and in waters surrounding the Hawaiian Islands.

In the spring of 1936, the heavy cruiser participated in Fleet Problem XVII, taking place off the west coast of the United States, Central America, and the Panama Canal Zone.

In May 1937, the Fleet again exercised in Alaskan waters and in the vicinity of the Hawaiian Islands and Midway, practicing the tactics of seizing advanced base sites - a technique later to be polished to a high degree into close support and amphibious warfare doctrines.

The division then sailed up the west coast of South America, visiting Valparaíso, Chile, and Callao, Peru, before transiting the Panama Canal and returning to Norfolk, where she arrived on 6 June.

Three days later, the heavy cruiser departed Norfolk and spent the remainder of September and most of October engaged in gunnery training and conducting exercises out of Guantanamo Bay and San Juan, Puerto Rico.

Departing Guantánamo on the latter day, the Tuscaloosa returned to Norfolk on 29 January and entered the navy yard there for special alterations to fit her out for service as presidential flagship.

On the next day, Tuscaloosa embarked President Roosevelt and his guests and departed in company with Jouett and Lang for a cruise to Panama and the west coast of Central America.

On 16 December, Roosevelt left the ship at Charleston, South Carolina, to head for Washington to implement his "lend-lease" idea—one more step in United States' progress towards full involvement in the war.

Soon thereafter, Tuscaloosa sailed for Norfolk and, on 22 December, embarked Admiral William D. Leahy, the newly designated Ambassador to Vichy France, and his wife, for passage to Portugal.

With the "stars and stripes" painted large on the roofs of Turrets II and III, and her largest colors flying, Tuscaloosa sailed for the European war zone, initially escorted by Upshur and Madison.

On 8 August, she departed Bermuda for Newfoundland and soon embarked General Henry H. Arnold, head of the Army Air Corps; Rear Admiral Richmond K. Turner, Director of the War Plans Division of the Navy; and Capt.

Augusta, bearing President Roosevelt, and her consorts soon arrived in the barren anchorage where the British battleship HMS Prince of Wales—with Prime Minister Winston Churchill embarked—awaited her.

Under the two-starred flag of Rear Admiral Robert C. Giffen, the Denmark Strait patrol worked out of wind-swept, cold Hvalfjörður, Iceland—nicknamed by the American sailors and Marines as "Valley Forge".

Tuscaloosa and Wichita "stripped ship" for war, removing accumulated coats of paint, interior and exterior, floor tiling, and other inflammable and nonessential items before they set out for sea on 5 November.

As the task force steamed toward Iceland, its warships were constantly alert to the possibility of an imminent sortie by the German battleship Tirpitz, the sister ship of the sunken Bismarck.

In his speech to the Reichstag declaring war on the United States, Adolf Hitler described the presence of Tuscaloosa at the scuttling of the Columbus two years prior as a hostile act against the German nation, insisting that it had forced the liner "into the hands of British warships".

She conducted refresher training out of Casco Bay and then underwent another brief refit at New York Harbor before joining Task Group 39.1 (TG 39.1), under the command of Rear Admiral John W. Wilcox, Jr., whose flag flew from the new battleship Washington.

TG 39.1 sortied from Casco Bay and then it struggled through the gale-whipped seas of the North Atlantic Ocean, bound for Scapa Flow, Scotland, in the Orkney Islands—the main base for the British Home Fleet.

On 8 November 1942, Operation Torch—the code name of the Anglo-American effort to conquer Northwestern Africa from the Vichy French and Nazi Germany, and thence to expel the Axis Powers from Africa—got under way.

As American troops waded ashore, Tuscaloosa's powerful 8-inch, 55-calibre guns, aided by accurate spotting from the cruiser's scout planes, thundered loudly and sent high explosive shells flying shorewards into the French Army's defensive positions.

After being narrowly missed by several torpedoes from Vichy French submarine Antiope and shells from Jean Bart's heavy artillery, Tuscaloosa retired from the battle scene to refuel at sea and to replenish her ammunition in deeper waters farther offshore.

After these laborious operations, she remained offshore in support of the invasion and then she headed back to the East Coast of the United States for a major shipyard overhaul and replenishment at a large naval base.

After leaving Boston, she escorted RMS Queen Elizabeth to Halifax, Nova Scotia, before rendezvousing with Ranger and proceeding to Scapa Flow to resume operations with the British Home Fleet.

On 2 October 1943, Tuscaloosa formed part of the covering force for Ranger while the carrier launched air strikes against port installations and German shipping at the seaport town of Bodø, Norway, in Operation Leader.

While ice "growlers" and pinnacles hampered antisubmarine screening by the destroyers' sound gear, Tuscaloosa fielded a party of 160 men on shore to unload supplies and equipment to reestablish the weather station.

Upon completion of the refit in February 1944, Tuscaloosa engaged in Fleet exercises and shore bombardment practice out of Casco Bay until April and then entered the Boston Navy Yard for installation of radio intelligence and electronic countermeasures gear.

Back in the vicinity of the Îles Saint-Marcouf on the evening of the 11th, she remained on station in the fire-support area until 21 June, providing gunfire support on call from her shore fire control party operating with Army units.

In September, when Allied forces had secured footholds in both western and southern France, Tuscaloosa returned to the United States for refitting at the Philadelphia Navy Yard.

Remaining until 3 November, she lay at anchor off the port, keeping well informed on the situation ashore through daily conferences with officials of the Communist Eighth Route Army.