After America entered World War I in April 1917, Missouri was brought back into service to train personnel for the expanding wartime Navy.

The class incorporated several significant technological developments, including smaller caliber main guns that used smokeless powder to achieve greater muzzle velocity (and thus penetrating power), Krupp cemented armor that was stronger than Harvey armor used on earlier vessels, and water-tube boilers that provided more power for the engines.

The ship was powered by two-shaft triple-expansion steam engines rated at 16,000 indicated horsepower (12,000 kW), driving two screw propellers.

As was standard for capital ships of the period, Missouri carried two 18 in (457 mm) torpedo tubes, submerged in her hull on the broadside.

She steamed out of Norfolk to begin her sea trials off the Virginia Capes on 4 February 1904 before joining the rest of the fleet in the Caribbean for training exercises.

An international fleet that included British, French, German, Japanese, and Austro-Hungarian warships joined the US Navy at the event.

[4] Missouri's next significant action was the cruise of the Great White Fleet around the world, which started with a naval review for President Theodore Roosevelt in Hampton Roads.

The press in both countries began to call for war, and Roosevelt hoped to use the demonstration of naval might to deter Japanese aggression.

[7] After leaving Australia, the fleet turned north for the Philippines, stopping in Manila, before continuing on to Japan where a welcoming ceremony was held in Yokohama.

The ships then crossed the Atlantic to return to Hampton Roads on 22 February 1909, having traveled 46,729 nautical miles (86,542 km; 53,775 mi).

[8] Missouri spent the next several years laid up, with periodic reactivations for summer training cruises for midshipmen from the US Naval Academy.

On 2 December, she was again decommissioned before returning to service on 15 April 1915 for a midshipmen cruise in the Caribbean, through the Panama Canal, and to visit ports in California.

Another period of active service began on 2 May 1916 for a training cruise along the east coast of the United States and into the Caribbean, before Missouri was again laid up late in the year.

Rear Admiral Hugh Rodman hoisted his flag aboard Missouri on 26 August, as the commander of the 2nd Division, Atlantic Fleet.