In the underwater world of submarine warfare, sound is the submariner's greatest enemy. The slightest noise, even the accidental drop of a cooking pot, can carry underwater for hundreds and thousands of miles and betray a submarine's location. Submarine hunters, listening through sonar devices, use sound to track submarines. Until this decade, the United States enjoyed a commanding lead in antisubmarine warfare (ASW), with submarines significantly quieter than Soviet counterparts. The Department of Defense says that lead has virtually vanished and Soviet vessels are harder to locate.
``The Soviets have closed the gap,'' John Lehman, then-Secretary of the Navy, told Congress earlier this year. ``Their new submarines are virtually as quiet as the subs we were planning to build just a few years ago.''
US defense officials have accused the Toshiba Machine Company of Japan for the setback. Toshiba and the Norwegian firm Kongsberg Vaapenfabrikk illegally sold the Soviet Union four computer-controlled milling machines designed to make very high-quality propellers.
An informed Pentagon source in Tokyo who spoke on condition of anonymity said a secret as sessment of the impact of the sale by the Defense Intelligence Agency and Naval Intelligence says that the Soviets have gained 7-to-10 years in propeller development. The US, they calculate, will need to spend $25-to-$30 billion on ASW over the next 15-to-20 years to counteract the gains the Soviets made with the Toshiba equipment.
In Tokyo, however, Japanese defense experts dispute the view that Toshiba Machines alone is responsible for helping to silence the Soviet submarines. Consequently, they question the justifiability of a recent 92-to-5 vote in the US Senate for a ban on all Toshiba imports for up to five years, and similar legislation pending in the House.
``Soviet submarines did not become quiet all of a sudden,'' wrote prominent defense critic Hideo Aoki recently.
``It was,'' he continued, ``1982-'83 when Toshiba first exported its milling tools to the Soviet Union, but Soviet submarines became quieter from around 1980. The United States has never clearly presented evidence of a concrete cause and effect relationship.''
A war-planning officer working in the US Defense Intelligence Agency said this view is widespread among Japanese military officers, including those in the Maritime Self-Defense Force. Even ASW experts ``are doubtful about the observation that the export of the Toshiba machines contributed significantly to the reduction of Soviet submarine noise,'' he said.
US defense experts agree that there are many reasons for improvement in noise levels. According to Norman Polmar, a naval analyst and author, the Soviets have made improvements in several areas:
Machinery, including engines and auxiliary machines, have been placed in mountings to muffle sound and reduce vibration.
Flow noises from the pumps supplying water coolant to nuclear reactors and from water passing around the hull have been reduced.
Propeller sounds diminished.
Much of this, the experts said, is the result of extensive technological progress by the Soviets, far greater than what was anticipated by Western intelligence. They said Soviet espionage and technology leaks from the West may have spurred some of the advances but the improvements were already well under way.
Mr. Polmar said that regardless of the extent of the recent damage from Soviet gains, ``in the long run the [Toshiba] machines will cause lots of problems.'' He said the Soviets will be able ``to produce high-quality propellers, much faster and much less expensive, and possibly quieter, than in the past.''
However, he said, it is ``highly unlikely that they had effect on the quieting of the latest class of Soviet submarines,'' the Sierra and Akula class attack submarines. The reason is purely one of timing. The submarines, according to Janes Fighting Ships, which is considered the handbook on war vessels, were launched by mid-1984 (in the case of Akula) at the latest.
The Toshiba machines, with their Norwegian numerical controls, were not installed and fully tested for use until the fall of 1984, according to Kazuo Kumagai, the former head of the Moscow office of Wako Koeki, a trading company that arranged the deal.
Two machines were installed in the Baltic Shipyard in Leningrad, according to Mr. Kumagai, who accompanied the Toshiba Machine Company technicians as an interpreter. That shipyard is involved only in producing surface vessels.
Kumagai said he believes the other two machines were installed simultaneously by the Soviets in the nearby United Admiralty Shipyard, where Sierra and older Victor class submarines have been built.
Soviet technicians watched each day's events at the Baltic Shipyard, reproduced them nearby at night, then returned visibly exhausted the next morning.
These facts suggest that while the Toshiba Machine sale was a significant security lapse, it may not completely account for the large-scale change in the balance of superpower submarine warfare.
The US is ``very upset at some developments in the Soviet submarine fleet,'' Polmar said. ``And we are looking for any excuse, other than the fact that the Soviets put a lot of time, effort, and money into the effort.''