On 21 May 1944, Fellers was transferred back to 5th Marine Regiment and succeeded temporary commanding officer, Lieutenant Colonel Henry W. Buse. Colonel Fellers supervised the training and preparation of the regiment for Peleliu operation; however, the division assistant commander, Brigadier General Oliver P. Smith (who personally served as 5th Marines Commander until 9 April 1944), was not satisfied with the way Fellers led the training of the regiment and how he treated the junior officers. Everything escalated after the complaint made by 5th Marines executive officer, Lieutenant Colonel Lewis William Walt, to Colonel John T. Selden. Selden, who served as 1st Marine Division Chief of Staff and was Walt's close friend, got a report that officers within the regiment were losing confidence in Colonel Fellers. The unofficial complaint was forwarded to General Smith, who decided to focus more on Fellers.