A little bit of History fluff on the Mandate Islands from Wiki
South Pacific Mandate
The South Sea Mandate (南洋庁 Nan’yō-chō?) was the Japanese League of Nations mandate consisting of several groups of islands (modern-day Palau, Northern Mariana Islands, Federated States of Micronesia, and Marshall Islands) in the Pacific Ocean which came under the administration of Japan after the defeat of the German Empire in World War I.
Under the terms of the Anglo-Japanese Alliance, after the start of World War I, Japan declared war on Germany on 23 August 1914 and participated in a joint operation with British forces in the Battle of Tsingtao to capture the German settlement in China’s Shandong Province. The Imperial Japanese Navy was tasked with pursuing and destroying the German East Asiatic Squadron and protection of the shipping lanes for Allied commerce in the Pacific and Indian Oceans.
During the course of this operation, the Japanese Navy seized the German possessions in the Marianas, Carolines, Marshall Islands and Palau groups, mostly without resistance, by October 1914.
After the end of World War I, as determined in the Treaty of Versailles, Japanese occupation of former German colonies in Micronesia north of the equator was formally recognized, and Japan was given a League of Nations Class C mandate.
In line with the terms of the mandate, Japan sought to incorporate the islands as an integral part of its empire, mounting aggressive economic development and immigration programs. Japanese, Okinawan and Korean immigrants eventually came to outnumber islanders by as many as two to one.
During the 1930s, the Japanese Navy began construction of airfields, fortifications, ports, and other military projects in the islands controlled under the mandate, viewing the islands as “unsinkable aircraft carriers” with a critical role to play in the defense of the Japanese home islands against potential American invasion. These became important staging grounds for Japanese air and naval offensives in the Pacific War. This work was done in secret, but this was not a direct violation of the Washington Naval Treaty as that treaty, by its own terms contained in Article XIX, did not apply to the Mandated Islands.
In addition to the islands’ naval importance, the Japanese Army utilized the islands to support air and land detachments. The “island-hopping” strategy employed by the United States military caused the Japanese Empire to lose control of its Pacific possessions between 1943 and 1945.
The League of Nations mandate was formally revoked by the United Nations in July 1947, and the United States was made responsible for administration of the islands under the terms of a United Nations trusteeship agreement which established the Trust Territory of the Pacific Islands
Saipan in the Marianas archipelago was the most important island militarily and economically in the South Pacific Mandate, and became the center of subsequent Japanese settlement. Another important island was Truk in the Carolines archipelago, which was fortified into a major navy base by the Imperial Japanese Navy.
The administration of South Pacific Mandate was managed by the Imperial Japanese Navy, which divided the region into six administrative districts reporting to naval headquarters in Truk. Later, in April 1922, civilian government was established in the form of a civil administration department which still reported to the local naval garrison commander in each of the six administrative districts: Saipan, Palau, Yap, Truk, Ponape and Jaluit Atoll.
Later, the headquarters of the South Pacific Mandate was transferred from Truk to Koror, Palau, and its governor reported directly to the Prime Minister of Japan. However, after the establishment of a Ministry of Colonial Affairs, the mandate’s governor was ordered to report to the colonial minister in June 1929.
When colonial affairs were absorbed into the Ministry of Greater East Asia in November 1942, the primacy of the Imperial Japanese Navy was again recognized by appointing an admiral as governor. Furthermore, the six administrative districts were reduced to three in November 1943: Marianas, Truk and Palau.
The population of the South Seas Mandate was too small to provide interesting markets and the indigenous people had very limited financial resources for the purchase of imported goods. The major significance of the mandate to the Empire of Japan was its strategic location, dominating sea lanes across the Pacific Ocean and providing convenient provisioning locations for sailing vessels in need of water, fresh fruit, vegetables and meat. Later, the islands became important coaling stations for steam-powered vessels.
The mandated territories produced significant quantities of sugar cane, bananas, pineapples, taro, coconuts, and other tropical farming products on a par with Taiwan. The islands also provided bases for the Japanese fishing fleet.
In terms of mineral products, many islands yielded phosphates for farming, especially from Angaur island, which produced some 60,000 tonnes per year. Bauxite was another segment of the colonial economic structure, although the mineral was only present in the Palau group. Large quantities of pearls, both natural and cultured, were extracted from the islands.
The islands also allowed for regular flight links for long range seaplanes such as the Kawanishi H6K2-L (“Mavis”) of Dai Nippon Koku KK.
Area of Japanese adminstered Mandate Isalnds