Ellis believed that US acquiescence to Japan's
South Seas Mandate, which allowed Japan to occupy islands that had previously been controlled by Germany, would enable Japan to operate behind a defensive screen to expand its territory and influence without being observed. Convinced that this course would eventually lead to war between Japan and the United States, Ellis determined to carry out intelligence gathering activities to obtain details on Japan's activities. On April 9, 1921, Ellis submitted a
pro forma request to the commandant to conduct a clandestine reconnaissance mission to the Central Pacific to examine the Marshall and Caroline Islands. His request indicated that he expected to travel as a civilian and to provide an undated resignation that would enable the Marine Corps to deny knowledge of his actions if necessary. (In fact, the Marine Corps did not use the letter of resignation, and retained Ellis on its roll of active officers until he died. At the time of his death, Ellis was listed in payroll and personnel records as being on "extended leave," a status the commandant had directed his staff to use.) Shortly after he submitted his request he suffered another occurrence of
neurasthenia; after recovering he asked to resume the intelligence mission in the Pacific. On May 4, 1921,
Assistant Secretary of the Navy Theodore Roosevelt Jr. approved the request as the acting Secretary of the Navy. Ellis left the hospital the same day, and reported to
Headquarters Marine Corps to finish making arrangements. To hide his identity as a military officer gathering intelligence abroad, Ellis turned to John A. Hughes, who was commissioned from the ranks with him in 1902. Hughes had been medically retired in 1920, after which he joined his father's import-export business, the Hughes Trading Company. Hughes provided Ellis with a cover identity as a traveling representative of the company. After a brief visit home to Kansas, Ellis traveled to San Francisco on May 28, 1921. Ellis ignored them, which essentially made him absent without leave (AWOL), cabled Marine Corps Headquarters for a draft of one thousand dollars he could receive at a local bank, and departed for
Saipan. Upon arrival aboard NBK Lines
Kasuga Maru, he debarked at the
Tanapag Harbor, and checked into a hotel in
Garapan with the intention of scouting the
Mariana Islands, which Japan was using as a central hub for their activities in
Micronesia. As Ellis continued his intelligence gathering mission and heavy drinking, he attracted the attention of the Japanese authorities, who began to keep track of his movements and activities. A friend, Kilili Sablan, suggested that Ellis check out of the hotel and live with the Sablan family. Ellis traveled around Saipan for several weeks, and produced detailed maps and charts. On December 3, 1922, he boarded the ship
Matsuyama Maru to travel to the Carolines, Marshalls,
Yap, and the
Palaus. Upon arrival, he checked into a hotel in
Koror, and again boarded the
Matsuyama Maru, intending to travel to
Truk; Ellis was unable to survey this island because Japanese authorities denied him passage, which was an indication that they remained suspicious of him. During a trip from
Kusaie, Ellis became ill aboard the
Matsuyama Maru and was hospitalized in
Jaluit by missionary Jesse "Mother" Hoppin who assigned her student Benjamin Lajipun to be Ellis' houseboy. After his recovery in January 1923, he continued to survey the Marshalls,
Kwajalein,
Ponape,
Celebes, and
New Guinea aboard the copra-collecting sailboat
Caroline Maru. Ellis slept on deck and took copious notes charting the reefs and inventorying local facilities, populations, and products. Japanese officials assigned Dr. Uichi Ishoda to watch Ellis on these voyages, and during a storm which nearly capsized
Caroline Maru Ellis demonstrated a knowledge of seamanship which caused Ishoda to conclude Ellis was a naval officer. While staying on
Koror, he met a teenage Palauan woman named Metauie, who became his wife. His friends attempted to keep him from drinking, but by then, he had a coterie of native boys who would obtain his alcohol for him. He continued to drink excessively, and his health continued to deteriorate. On May 12, 1923, he was unable to obtain any alcoholic beverages as the result of his friends attempting to keep him sober, and he unsuccessfully looted the home of his friend William Gibbons in search of drink. Aware of Ellis's condition, the Japanese police had two bottles of whiskey delivered to him; he consumed them both, and died later the same day from the effects of excessive alcohol intake. ==Ellis' death==