[3] A large, athletic man, he was nicknamed "Big Charlie" and maintained a notably fit appearance even during the late stages of his career.

[3] Thompson served at West Point as assistant athletic officer from August to December 1907, after which he rejoined the 13th Infantry at Fort Leavenworth, Kansas.

[7] From June to August 1917, Thompson was assigned to the 38th Infantry in Syracuse, New York as it organized and trained in anticipation of U.S. entry into World War I.

[7] He was promoted to temporary major on August 5, then assigned as a small arms instructor at Fort Sill, Oklahoma.

[7] From September to December 1917, Thompson was adjutant and assistant chief of staff of the 82nd Division as it completed its organization and training at Camp Gordon, Georgia.

[7] After arriving in France in February 1918, Thompson was assigned to the Intelligence staff section (G-2) of the American Expeditionary Force headquarters.

[9] Using his own assets and analysis, Thompson created and disseminated a graphic intelligence summary portrayed on a 1:100,000 scale map that broke down into regimental sectors the disposition of the eight German divisions facing Second Army.

As Assistant Chief of Staff, G-2, of the 1st Army, Lieutenant Colonel Thompson aided in its organization by his skill and sound judgment, participating in the preliminary preparations and operations at the St. Mihiel salient.

The successes achieved by his section are largely due to his high military attainments, his great energy, and painstaking devotion to duty.

He served with equal ability as G-2 of the 2d Army in September 1918, at all times showing great skill and accomplishing results of exceptional value.

[12] After returning to the United States, Thompson was assigned to the West Point faculty as an instructor in the Department of Tactics.

[12] Thompson was assigned as assistant to the chief of staff for the Fifth Corps Area at Fort Benjamin Harrison, Indiana in September 1920.

[12] In August 1921, Thompson was part of the contingent of troops that attempted to restore order among striking coal miners in West Virginia and he testified at the May 1922 trial of organizer Bill Blizzard.

[12] In August 1924, Thompson began attendance at the United States Army Command and General Staff College, which he completed as a distinguished graduate in June 1925.

[14] In July 1929, Thompson was assigned as executive officer of the 30th Infantry Regiment and the post headquarters at the Presidio of San Francisco.

[14] He returned to the United States in May 1934 and was assigned as an Army Reserve advisor for the Ninth Corps Area, based at the Presidio of San Francisco.

[15] He was promoted to major general in October 1940, and led the division during its organization and training prior to entering combat for World War II.

[16][17] In addition, Thompson's command was responsible for handling the administrative, logistical, and training requirements of arriving U.S. military units, ensuring they were prepared to enter combat in the Pacific theater.