Colonel Cumming was appointed commanding officer of 25th Marine Regiment at the end of July 1943. He relieved Colonel Richard H. Schubert in command of the regiment and continued in the extensive training. He and his men subsequently sailed to Camp Pendleton, California, via the Panama Canal and arrived there on September 10, 1943. Cumming and his regiment were then attached to 4th Marine Division under Major General Harry Schmidt and began with the preparations for the upcoming Kwajalein Operation.