Japan is an unsinkable aircraft carrier obstructing Soviet access to the open ocean -- westward, toward the North American continent, and southward, to the Indian Ocean and the oil link with the Persian Gulf.
AS the United States redeploys its naval forces in the wake of the Iranian and Afghan crises, defense experts here point to Japan's geostrategic position as the key to the defense of the western Pacific against expanding Soviet naval and air forces.
"We could be just as strong industrially and economically as we are today," said one leading defense planner, "and I don't think we'd be half as valuable to the West if our islands were just a bit further from the Soviet Union."
He and other defense planners focus on two areas -- one where Japan's geographic advantage is clearly apparent, another where the Soviets must be trying to outflank this position.
The first is the Sea of Okhotsk and the choke point that leads into it -- La Perouse Strait between Hokkaido and Soviet Sakhalin. The other is Vietnam, far to the south.
The Sea of Okhotsk is important to Moscow for two reasons. It is nearly a Soviet lake -- Hokkaido is the only non- Soviet territory fronting on it. Soviet Delta-class ballistic missile submarines can fire their nuclear-tipped missiles at almost any American target from under the protected waters of this sea.
Overhead, Backfire long-range bombers newly assigned to the Far East can cross over Sakhalin from their base somewhere in the Soviet maritime province, proceed straight down the Sea of Okhotsk off Hokkaido. After refueling over the southern Kuriles (claimed by Japan, occupied by Moscow), they can then range widely over the Pacific Ocean -- as far as to the Phillipines or to Hawaii.
Defense experts estimate about 17 Backfires are stationed in the Far East at the moment. They pose of formidable new threat to battle groups of the US Seventh Fleet, hitherto geared mainly to repelling submarines.
But if the Japanese, with US help, can establish control over La Perouse Strait, they can cut the Soviet sea lane from Vladivostok across the Sea of Okhotsk to the ice-free submarine base of Petropavlovsk fronting on the Pacific Ocean. American and Japanese fleet units penetrate the Sea of Okhotsk at least once a year, just to show Moscow that it remains an open sea.
Furthermore, by denying the Soviets the Tsugaru Strait between Hokkaido and Honshu (the main island), and the Korea Strait between Japan and South Korea, the entire Soviet Pacific fleet could effectively be bottled up in the narrow Sea of Japan.
As Japan's defense capacity grows, it is expected to concentrate more and more of its efforts on Hokkaido and La Perouse Strait -- efforts that not only uphold the defense of Japan but also contribute to that of the US and of the entire Western position.
In contrast to the Sea of Okhotsk, Vietnam is an area about which the Japanese can do little. As the Indian Ocean becomes a focus of superpower conflict, both the Soviets and the United States have stepped up their naval presence in the area, so vital to the supply of oil, not only for Japan, but also for Western Europe and North America.
But in contrast to the US, which has a naval base at Subic Bay in the Philippines and an air base at Clark Field in the same country, the Soviet so far have no permanent facility close to the Indian Ocean. Most Soviet ships in the Indian Ocean come from the Pacific fleet, and their supply line to their base at Vladivostok is long and precarious.
Soviet air and naval bases in Vietnam would change all that. They would enable the Pacific fleet to escape being bottled up in the Sea of Japan. They would directly threaten Subic Bay and Clark Field and menance Japan's essential trade route from the home islands to the Middle East oil fields.
Vietnam insists it will not grand permanent air and naval bases to the Soviet Union. But the Southeast Asian situation is volatile China is also involved, and if confrontation between the superpowers intensifies, no one can be certain where move and countermove on the international chessboard may lead.