The Japan Maritime Self Defense Force (Nihon Kaijyo Jieitai) conduct two kinds of operations for the purpose of defending Japan: securing maritime traffic and securing Japanese territory. For Japan, which relies on foreign countries for the supply of almost all energy and food, the repercussions of that supply line getting cut would have a severe effect on almost all aspects of Japanese life. It can also be said that the impact to the world economy is significant in such case. Therefore, the JMSDF must be able to secure maritime traffic against attack by enemy submarines, surface ships and aircraft by effectively combining each operation such as surveillance, escort and defense of ports and straits. In case of aggression that aims at territorial occupation, it is necessary to stop it at sea in order to prevent direct damage to the territory. For that purpose, the JMSDF, in cooperation with the JGSDF and the JASDF, contributed to the defense of Japan during WWIII by destroying enemy surface ships, aircraft, and laying mines around the expected landing zones.
The nation is vitally dependent on maintaining access to regional and worldwide shipping lanes and fishing areas, but it is incapable of defending the sea routes on which it relied. Its energy supplies came primarily from Middle Eastern sources, and its tankers had to pass through the Indian Ocean, the Strait of Malacca, and the South China Sea, making them vulnerable to hostilities in Southeast Asia. Vulnerability to interception of oceangoing trade remained the country's greatest strategic weakness.
The large volume of coastal commercial fishing and maritime traffic limits in-service sea training, especially in the relatively shallow waters required for mine laying, mine sweeping, and submarine rescue practice. Training days are scheduled around slack fishing seasons in winter and summer--providing about ten days during the year. The JMSDF maintains two oceangoing training ships and conducts annual long-distance on-the-job training for graduates of the one-year officer candidate school.