During February 1933, Kamoi is converted to a seaplane tender at Tokyo Uraga Dock Company completed by June 1, 1934, capable of carrying twelve Kawanishi E5K1 three-seat reconnaissance floatplanes tail code “5-xx”, or 22 stored as cargo and can also operate as an oilier.
During September 25, 1935 "Fourth Fleet Incident" Kamoi is caught in a typhoon when other ships are damaged (unknown if Kamoi was damage).
On January 28, 1937 departs Yokosuka with Okinoshima with destroyers Asanagi and Yunagi for Carolines and Marianas to survey the sites for potential military bases. The group visits a total of 21 ports and also surveys 11 locations from the air for sites that can be used as future airfields, and returns to Yokohama by June.
During June 29 - July 5 1937, participates in maneuvers with Yokohama Kokutai, along with Okinoshima, Asanagi and Yunagi.
After Emperor Hirohito's younger brother, Prince Nobuhito Takamatsu, a staff officer at the Naval General Staff, received the news Amelia Earhart’s Model 10 Electra disappearance, he persuades Japanese Navy Fleet Admiral, Prince, Fushimi Hiroyasu to order Kamoi to search for Earhart. But the order to Kamoi contains no information about where she was lost and a few hours later, the order is canceled. Note: other sources erroneously place Kamoi at Saipan on July 3, 1937.
On July 6-8, Kamoi was at sea bound for Futami on Chi Chi Jima on July 6-8, and July 8 headed for Ise Bay.
On July 19, 1937 arrives Ise Bay, then during August returns to northwest Formosa, then to Shanghai. On October 12, 1937 two E8N2 Dave floatplanes from Kamoi take off on a reconnaissance mission over Nanking. Intercepted over the target, one is lost during a collision with a Curtis Hawk, the other is damaged and lands on the Yangtze River, but is strafed and sunk.
During May 1938, supported Japanese operations off Kulangsu Island and during August operated on the Yangtze River against the Chinese, and participates in the October 12-25 attacks against Canton. During October 1939, departs China and is assigned to the newly established 4th Fleet at Truk Lagoon during November 1939.
During 1940, refitted as a seaplane tender. In January 1940, Kamoi with Chitose and Kinugasa Maru travel to Truk Lagoon with construction materials to build Dublon Seaplane Base, making several trips to Japan for more materials. Afterwards, searches Roi, Wotje and Jaliut Emidj for future seaplane base locations in the event of war and to provide service for the Yokohama Kokutai seaplanes.
On January 28, spotted by USS Bowfin SS-284 and tracked, but forced to evade her seaplanes. Surfacing at 2100, the sub fires six torpedoes, but all miss. At 2329 fires two more torpedoes, both hit damaging the ship and taking on water near the bow. A final torpedo fired misses, and closes on the surface, but is fired on. At 2348 the sub fires a final torpedo that hits between the bow and bridge, forcing the ship to beach to prevent sinking.
On January 29, towed to Surabaya for emergency repairs by 102 Repair unit, then departs for Singapore and undergoes repairs at Seletar Navy base starting on February 1. On April 15, the seaplane gear is removed, converting the ship as a fuel tanker only. Conversion is completed by August 29 at Singapore.
On September 6, departs Singapore in a convoy with Kyokuto and Okigawa Maru escorted by destroyers Satsuki and subchaser CH-30 and CH-33. Arrives at Miri on September 8. On September 15 departs for Manila Bay with another larger convoy, but detaches from the convoy at Bacuit Bay, Palawan and proceeds to Coron Bay.
On September 24, while in Coron Bay, attacked by USN aircraft and Kamoi is damaged, but escapes to the open sea, returns to Bacuit Bay on September 25 and proceeds to Manila Bay with another convoy, but instead the convoy goes to Takao.
Still damaged and proceeding slowly, Kamoi is attacked on September 27 by USS Bonefish SS-223 and hit by one of four torpedoes, and further damaged roughly 240 miles southwest of Manila Bay. On September 29 arrives at Manila Bay and emergency repairs are made at Cavite Navy Yard, then departs for San Fernando with another convoy, departing October 6. The same day, the convoy is attacked by USS Aspuro SS-309 and USS Cabrilla SS-288. The convoy arrives at Lapoc Bay at 1830.
On October 7, warned of US Navy activity, the convoy splits, with Kamoi and other ships departing for Yulin, China. At 600, Kamoi with Tachibana Maru and subchaser CD-8 proceed alone. The warning is cancelled and the ships proceed to Takao as planned, but on October 9, Tachibana Maru is sunk at night by a torpedo attack by USS Sawfish SS-276 and damages CD-8. The next night, the sub sinks Tachibana Maru. Departing alone, Kamoi proceeds to Hong Kong, arriving alone and is dry docked for extensive repairs by 2 Repair Unit.
Damaged during an air raid on November 5, 1944, but repairs continue then departs for Japan.
On December 31, departs Japan with another convoy leaving form Moji for Singapore via Takao and Manila Bay, but the convoy holds at Chusan Islands on January 3-5, 1945 due to threats of attacks. Proceeding, the convoy is attacked by US Submarines. On January 8 anchors at Takao, then departs on January 10 for Mako, Pescadores, but is diverted to Hong Kong instead due to air attacks.
During January 15 air attack, damaged at Hong Kong. On January 16 suffers a near miss from a US Navy aircraft at 1124 and at 1240 a direct hit in the engine room immobilizing the ship. Later that day, P-51st strafe Kamoi and start fires.