The Iran-Iraq war is adding new fuel here to the argument that Japan should upgrade its defense capabilities in an area where it has vital commercial interests.
Although the government foresees no immediate impact resulting from the fighting, the possiblity of it escalating to the point of closing the Strait of Hormuz has underlined the country's economic and military vulnerability.
"Closure of the strait would shake the very foundations of the Japanese economy," one senior official admitted.
The Japanese, undoubtedly, would suffer far more than any other nation from the waterway's closure. Fully 70 percent of the country's oil passes through the strait. Two-thirds of all the vessels passing through it fly the Japanese flag.
So far, however, the government has remained remarkably calm. The country has survived without Iranian crude, which was cut off after Japan joined in the sanctions against Tehran over the US Embassy hostage incident.
Iraq currently supplies 8.5 percent of Japan's needs. But even if their supply is halted for some time, government officials believe the nation can easily cope.
The country has enough oil stockpiled to last 111 days at present consumption rates -- and is now using about 300,000 barrels a day less than originally anticipated.
At the same time, however, government officials are painfully aware that a closure of the Strait of Hormuz could wipe out 60 percent of the emergency oil stockpile within two months. The US already has warned the Tokyo government of the implications of a wider Gulf war.
US Undersecretary of Defense Robert W. Komer used it as an argument for a major improvement in Japanese defense capability during a Sept. 22 meeting with Foreign Ministry officials.
He reportedly pointed out that the relocating of the US 7th Fleet from the Far East to the Indian Ocean to counter the Soviet's presence in Afghanistan has left a vacuum in the area.
That vacuum, Mr. Komer is believed to have said, can only be filled by Japan. The US defense official noted that while Tokyo is concerned about a possible Soviet invasion from the north, a more likely danger is severance of its Gulf oil route.
Despite its preponderance of commercial ships in the Gulf, Japan is contitutionally prevented from sending in any of its Navy vessels to offer protection.
The Constitution specifically forbids the dispatch overseas of defense forces in any capacity (including as part of a United Nations peace-keeping force). Even the present dangers seem insufficient to persuade the government to risk opening a Pandora's box of constitutional revision.
But even if there were changes, the country doesn't have enough ships to ensure protection of its commercial fleet. Thus Japan would have to ask the United States to escort its tankers in an emergency. And Japan, it is being argued, could hardly do this unless it was prepared to meet repeated US requests to upgrade its defense forces and contribute more to regional security.
President Carter last week proposed an international surveillance fleet to ensure freedom of navigation through the Strait of Hormuz. (Japan would be involved in decisionmaking but not in the actual operation.)