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strained.  Opponents disagree, saying that cheating under

the CTBT can go undetected.

The CTBT Is Not Verifiable

Throughout the history of test ban negotiations, U.S.

policy consistently stated that the United States would

not sign any treaty unless it were effectively verifiable.

The reason for this position is that any adversary that

covertly tests--while the United States forgoes testing--

can gain significant military advantage.  Testing both

allows nuclear weapons modernization and confirms stockpile

reliability.

Effective verification is generally accepted to mean

high confidence that militarily significant cheating will

be detected in a timely manner.  In the case of the CTBT,

this would mean that the United States would have high

confidence that it would be able to detect, within hours

or a few days of the event, any nuclear test that would

provide the testing nation with militarily significant

weapons information.  Two key questions must therefore be

addressed: what is the minimum yield of a nuclear test

that can provide militarily significant information, and

can the CTBT verification system detect tests at that

level?

Testing at 500 Tons of Yield or More Provides Militarily

Significant Data

Testing at any yield, regardless of how low it is,

may provide militarily significant information to a prolif-

erator and, perhaps, to an advanced nuclear weapons state.

In the case of the United States, the lowest possible

yield to accomplish new designs, as well as ensure safety

and reliability, depends upon warhead requirements.  Most

designs could be adequately tested at yields between 1 and

10 kilotons.10   A yield of only 500 tons would be suffi-

cient for testing the reliability of U.S. nuclear weapons,

but a higher yield would be needed to certify any new

design that departed significantly from already tested

designs.  Therefore, it is reasonable to assume that 10-

kiloton tests would be militarily significant--meaning that

they could prove the reliability of weapons--and that

tests down to a level of 500 tons might also fit into this

category.11