[7] The 24th Infantry was mobilized for the Spanish–American War in April 1898, and Leitch was with the regiment during organization and training at Chickamauga Park, Georgia and in Tampa, Florida.

[7] As commander of Company B, and later as acting regimental adjutant, Leitch served in Cuba during the summer of 1898, including the Battle of San Juan Hill and Siege of Santiago.

[7] Leitch contracted yellow fever in late July 1898, and remained at a convalescent camp in Siboney, Cuba until September 1898.

[7] He was demobilized at Camp Wikoff, New York at the end of September and returned to duty at Fort Douglas in October.

[7] Leitch took command of 1st Battalion, 25th Infantry at the Presidio of San Francisco in September 1900, and traveled to the Philippines with his unit to take part in the Philippine–American War.

[7] From May 1904 to July 1906, Leitch served again at Fort Niobrara, and he was the 25th Infantry's regimental commissary officer from August 1904 to June 1906.

[7] From October 1915 to January 1916, Leitch commanded 3rd Battalion, 27th Infantry at Camp Grant, Balboa, Panama Canal Zone while awaiting travel to the Philippines.

[7] He commanded the battalion at Fort William McKinley, Philippines from March to October 1916, and he was promoted to lieutenant colonel in the 8th Infantry on July 1, 1916.

[7] After returning to the United States, Leitch was assigned to command the 40th Infantry Regiment at Fort Snelling, Minnesota, and he served from June to August 1917.

[7] Leitch served in Russia from May 1919 to March 1920, first as inspector general, and later as chief of staff of American Expeditionary Force, Siberia.

[7] From June 1925 to March 1926, Leitch was stationed at the Presidio of San Francisco as liaison to ORC units based in northern California.

[7] From April 1926 to January 1927, Leitch commanded 8th Brigade, 4th Infantry Division and the post of Fort McPherson, Georgia.

[7] From February to October 1927, Leitch commanded 5th Brigade, 3rd Infantry Division and the post of Vancouver Barracks, Washington.

As Chief of Staff of the American Expeditionary Forces in Siberia, Colonel Leitch gave proof of his great breadth of vision, keen foresight, sound judgment, and tact.

By his brilliant professional attainments, coupled with great diplomacy, he handled most ably the many delicate situations with which he was confronted.

His fine soldierly qualities were at all times outstanding, and by his masterful grasp of the situation he was able to meet successfully each new and difficult problem with which he was faced.

He rendered most conspicuous services of inestimable value to the Government in a place of great responsibility and at a time of gravest importance.

[9]In addition, his Russian service resulted in award of the Order of Saints Maurice and Lazarus (Officer) from Italy and the Cross of War from Czechoslovakia.