Busload of Megatons

THE standard ballistic missile carries only one nuclear warhead. That has long seemed inefficient to Pentagon planners, considering the huge cost of missiles and the space required to store them. In the early 1960s, they developed the first improvement: a multiple warhead known as MRV (for Multiple Re-entry Vehicle). It is a relatively crude device that drops unguided from missiles in clusters of three warheads. Some MRVs have been placed on presently operational Polaris missiles. A further and major refinement is MIRV (Multiple Independently Targetable Re-entry Vehicle), which is similar to MRV but has its own propulsion and guidance systems.

Missiles equipped with the MIRV device have been compared to a space bus that travels above the atmosphere emitting warheads over specific targets. MIRVs could be carried only by the next generation of missiles--the Navy's Poseidon and the Air Force's Minuteman III, which will probably be operational within two years. Both have been successfully tested with MIRVs.

> The Minuteman version, with a range of 7,500 miles, carries up to three warheads (each under one megaton) and some chaff that is released to confuse enemy anti-ballistic missile radar. Present plans call for deployment of 500 MIRVed Minuteman Ill's, in addition to 500 Minuteman II's with single warheads. All would be housed in 90-ft.-deep silos, located at least seven miles apart to prevent an enemy warhead from destroying two sites.

> The Poseidon version can carry up to twelve warheads and has a 2,900-mile range. The Poseidon MIRVs are thus of the "low kiloton" type, designed to be used against cities, while the Minuteman Ill's might be used to hit the adversary's iCBMs in hardened silos. The Navy has begun to refit two of its Polaris submarines to handle Poseidons. According to present plans, 496 of the 656 missiles now aboard submarines will carry MIRVs.

Accordingly, by the mid-1970s the Navy and Air Force could be capable of launching a total of more than 8,000 warheads, compared with 2,700 presently.

The Russians, meanwhile, have completed a series of multiple-warhead test shots in the Pacific. A U.S. destroyer monitoring the tests reported that the S59 missile, which had never before flown more than 3,200 miles, is now capable of reaching most of the U.S. The reconnaissance vessel also learned that before the S59 splashed into the Pacific, the missile delivered three separate warheads. Since the SS-9, with a multiple warhead, can carry up to 15 megatons, Defense Department officials warn that it is a serious threat to U.S. missile installations. A five-megaton blast within a mile of a missile silo will destroy it.

Defense Secretary Melvin Laird has said that the Russians are not yet capable of launching MIRVs. But in his press conference last week, President Nixon hinted that the Soviets have developed some sort of control system for their MRVs.

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Intelligence reports have shown that the SS-9's reentry vehicles splashed down in a pattern. That design, when superimposed on a map of U.S. missile sites, was found to coincide with the distribution of ICBM silos. "There isn't any question," Nixon said, "that it is a multiple weapon, and its footprints indicate that it just happens to fall in somewhat the precise area in which our Minuteman silos are located."

The President's "footprint" statement was yet another disclosure of normally secret intelligence material to bolster the chances for approval of the embattled ABM. For the White House regards its Safeguard anti-ballistic missile system as the answer to the presumed Russian MIRV threat. Among his other warnings, Secretary Laird has said that the Russians are developing an ABM system of their own that can "loiter for a period of time until a specific target is selected."

More significant than stray tidbits of security data, of course, are the calculations of just what kind of weapons the Russians will actually build, and in what numbers. On this crucial point, the experts seem to disagree.

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