[1] During November of that year, Pepper was attached to the 1st Provisional Marine Brigade under the command of John H. Russell Jr. and sailed for his first expeditionary duty in Haiti.

[1] In April 1922, Pepper was ordered back to Caribbean and appointed Aide to the American High Commissioner in Haiti, Brigadier General John H. Russell.

[2] Lieutenant Colonel Pepper left Washington, D.C. in June 1939 and returned to the Parris Island, where he assumed duties as commanding officer of 1st Battalion, 15th Marine Regiment.

He then spent next year with extensive training and then sailed for Pearl Harbor in April 1940. Pepper was replaced in command by Colonel Harry K. Pickett at the end of August 1940 and subsequently took part in the preparation of defense at Midway Atoll.

During the Japanese Attack on Pearl Harbor on 7 December 1941, Pepper sailed together with Colonel Gilder D. Jackson Jr. aboard the heavy cruiser USS Indianapolis to Johnston Atoll to observe the testing of new Higgins boat.

[1][2] Pepper was promoted to the rank of colonel in May 1942 and his unit subsequently sailed to Guadalcanal at the beginning of August 1942 in order to reinforce 1st Marine Division under Major General Alexander Vandegrift.

[1] He later took part in the Battle for Henderson Field at the end of October 1942 and his battalion defensed the Lunga Point against the enemy counterattack from the sea.

[3][1] Pepper was subsequently transferred to the staff of the 11th Marine Artillery Regiment located in Australia for rest and refit after heavy combats on Guadalcanal.

He relieved Colonel Pedro del Valle as commanding officer on March 29, 1943, and led his regiment to New Britain in December of that year.

This facility served as boot camp, and Pepper was co-responsible for the training of replacement troops for the marine units deployed overseas.

He was responsible for the training of new recruits for next year and half and subsequently relinquished command to his deputy, Brigadier General Matthew C. Horner at the end of January 1952.

[1] He was transferred to San Francisco at the end of September 1955 and relieved Major general Henry D. Linscott as commander of Department of the Pacific.

[1][2] His retirement did not last long, because Pepper was recalled to active duty in July 1960, when he was appointed Marine Corps member of Bolte Committee, which was tasked to study Officer Personnel Act from 1947.