It was the primary opponent of the Western Allies in the Pacific War. The IJN additionally fielded limited land-based forces , including professional marines , marine paratrooper units, anti-aircraft defense units, installation and port security units, naval police units, and ad-hoc formations of sailors pressed into to service as naval infantry.
The origins of the IJN date back to early interactions with nations on the Asian continent , beginning in the early feudal period and reaching a peak of activity during the 16th and 17th centuries at a time of cultural exchange with European powers during the Age of Discovery.
This eventually led to the Meiji Restoration. Accompanying the re-ascendance of the Emperor came a period of frantic modernization and industrialization. Japan has a long history of naval interaction with the Asian continent, involving transportation of troops between Korea and Japan, starting at least with the beginning of the Kofun period in the 3rd century.
Japan undertook major naval building efforts in the 16th century, during the Warring States period when feudal rulers vying for supremacy built vast coastal navies of several hundred ships. Japan built her first large ocean-going warships in the beginning of the 17th century, following contacts with the Western nations during the Nanban trade period.
For more than years, beginning in the s, the Japanese policy of seclusion " sakoku " forbade contacts with the outside world and prohibited the construction of ocean-going ships on pain of death.
