From the standpoint of sea power, Japan's survival in case of war is ''as vital to the United States as it is to Japan,'' says Vice-Adm. M. Staser Holcomb.
Admiral Holcomb commands the US Seventh Fleet, with a defense mission that extends from the Sea of Okhotsk to the Indian Ocean. It is a vast area, and ''Japan is the key,'' the admiral says crisply.
Faced with a common threat from a steadily expanding Soviet Navy, Japan and the United States need each other as never before, in the admiral's view. Without American support, Japan could not survive against Soviet attack, and in turn, Japan's active support is essential to the admiral's wartime task of blockading and destroying the Soviet Pacific fleet.
In an interview aboard his flagship, the USS Blue Ridge, moored here, the lean, taut admiral made clear he was talking about a contingency he hoped would never arise.
''When I look at the defense picture,'' said the admiral, pointing to a Mercator map of the world that covered one wall of his office, ''the only real threat is the Soviet Union. The only context in which the threat becomes real is a worldwide conflict with the Soviet Union.''
In such a conflict, Japan's vital interest would be to keep open the sea lines of communication upon which its survival depends, at least out to a distance of 1,000 miles. The formidable offensive might of the US Seventh Fleet could then operate with relative security from the Pacific lee of these strategically placed islands to bottle up the Soviet fleet in the Sea of Japan, and eventually to destroy it. Japan is the key precisely because it lies athwart the three straits leading out of the Sea of Japan into the open ocean. The Soviet Pacific fleet's two main bases are Vladivostok on the Sea of Japan, and Petropavlovsk on the Pacific Ocean side of the Kamchatka Peninsula.
Vladivostok, at the end of the trans-Siberian railway, has all the infrastructure the Soviet fleet requires. But Petropavlovsk is isolated and supplies can reach it only by sea. The more solid the defense of Japan's own islands becomes, the greater the possibility of closing the straits to Soviet ships, of keeping Soviet bombers from flying over Japanese territory to attack American naval targets in the Pacific.
Thus, in Admiral Holcomb's view, American and Japanese defense interests complement each other. ''The Soviet Navy is a threat to the security of Japan and to the vital interests of the United States,'' he said. ''These two are inseparable.'' The US has been urging Japan to step up the pace of its defense buildup, and indeed Admiral Holcomb says Japan could spend two or three times what it is budgeting today without changing the essentially defensive nature of its buildup.
But even today, with 48 surface ships capable of antisubmarine operations, some degree of sea-lane defense is possible. The Japanese goal is to increase its antisubmarime-warfare surface ships to 60 and to vastly improve air surveillance and early warning capability by procuring 50 P-3C Orion antisubmarine aircraft and eight E-2C Hawkeye aircraft.
Meanwhile the Soviets have been increasing their use of Cam Ranh Bay in Vietnam, where on any given day a dozen Soviet ships may be seen at anchor, featuring a hard core of support and repair ships, plus cruisers, destroyers, submarines, and other craft going in and out.
''It's a terrible irritant in our side, as compared to five years ago,'' Admiral Holcomb said. ''The Soviets have moved in, have increased their presence , and thus have clearly affected the naval balance in the area. They can sail out of Cam Ranh to the Indian Ocean as fast or faster than we. They are astride one of our major sea lines of communication.''
At the same time, in an actual war, Admiral Holcomb thinks the Soviet presence in Cam Ranh is vulnerable. ''Their (the Soviets') weakness is that they have to come by sea, and we are better at that than they. Their forces will be vulnerable as tension rises and the shooting starts.''
Cam Ranh also faces the American naval base at Subic Bay in the Philippines. With negotiations on extending American use of Subic and of Clark Air Base about to begin between the US and the Philippines, Admiral Holcomb did not want to be drawn out regarding how much Subic is worth to the US Navy. Without Subic, the Navy would have to fall back to Guam, 1,000 miles east. A naval strike force could certainly operate out of Guam, but the cost would obviously be far greater than of operating out of Subic Bay.
Meanwhile, the Seventh Fleet is to be strengthened by the arrival of the battleship New Jersey, outfitted with 32 Tomahawk land attack missiles and 16 Harpoon antiship missiles. The Seventh Fleet has on average 21/2 aircraft carriers assigned to it. The New Jersey, with long-range cruise missiles, will be ''like another aircraft carrier,'' Admiral Holcomb said. It is expected to add great flexibility to the fleet because it can operate as part of a carrier task force, or as the centerpiece of its own task force, or in the more classic battleship role of supporting amphibious landings.