The atolls of Micronesia are ideally suited for sea-plane operations.
Atolls are rings of coral reef usually with a large and quite calm lagoon in the middle.
The islands on the windward side of the reefs provide a an ideal plane anchorage on the leeward beach, sheltered from wind and waves. The lagoon is usually clam enough to permit unrestricted landing and take-off of larger flying boats, and so it is not surprising that the lagoons were used as seaplane bases first by civilian and later by military aviation. The first irregular air service flying Yokohama, Saipan and Palau opened in 1935, after successful test flights had been carried out in 1934 . The Annual Report of the South Seas Government, the Japanese administration of Micronesia, for the year 1938 states that the airline Dai Nippon Koku Kaisha began and air service connecting Japan with Saipan and Belau. In 1939 Pohnpei and Jaluit were added.