From so simple a beginning…

When on May 11, 1998 India tested nuclear explosives, there was considerable doubt about whether we had tested a bona fide thermonuclear or hydrogen bomb. Every country’s strategic nuclear deterrent has thermonuclear weapons, and to announce itself as a ‘true’ nuclear weapons power India had to demonstrate that we had the capability to build hydrogen bombs. However most outside sources did not believe we had tested a true thermonuclear.

Curiously we seem to have largely bluffed then about the yield, and now the debate seems to have been ignited again with a statement by P. Santhanam of the DAE who accepts that our purported thermonuclear might have fizzled out. Surprisingly, at the same time there seem to be statements from individuals as august as A P J Abdul Kalam who contends that the tests provided the “designed yield”.

Interestingly, Santhanam does not seem to offer any perspective about what the yield actually was. However, calculations and measurements done at the time seem to leave little doubt that the design fizzled out. It’s worth reviewing this analysis.

There seem to be three dominant sources which converge on a consensus that India’s purported thermonuclear test failed to work.

The first source is the Federation of Atomic Scientists, whose analysis indicated a yield of between 12-25 kT

The second source is nuclear specialist Robert Norris who analyzed data from sixty-two seismic stations and concluded a yield of 12 kT

The third source is the UK’s Atomic Weapons Establishment who compared the signals from the 1998 test to the 1974 ‘Smiling Buddha’ test. Comparing signal strength they arrived at a rather accurate estimate of 16 kT for the total yield.

Using an average estimate of 16 kT, we can apportion the energy between the three devices that India tested. Shakti 1 was supposed to be the thermonuclear. The second device (Shakti 2) was supposed to be a weaponization of the 1974 experiment and therefore we can be quite confident that we got the yield right and as announced- about 12 kT. Shakti 3 whose purpose was to generate interesting data released a relatively negligible 0.2 kT.

Simple subtraction leaves about 4kT for the ‘thermonuclear’ Shakti 2.

Now of course at the time, the Indian government talked about a yield of 45kT from Shakti 2. The design was supposed to be a classic Teller-Ulam kind of design in which a primary fission trigger ignites a secondary fusion package. However most experts now think that what happened was that the primary only partially detonated and delivered the 4kT, and with such a small yield the secondary simply failed to ignite. As painful as it sounds, this means that the device did not work at all as intended and was an embarrassing failure. Even the error estimates don’t leave too much room to wriggle.

However, what repurcussions this has for India’s nuclear deterrence is a different matter. I agree with some others that we should not have bluffed at the time. After all no country (except probably China) has really gotten it right the first time. Also, deterrence does not depend on the mere existence of hydrogen bombs but depends on a complex system of nuclear weapons and delivery systems. It’s worth recalling that many rather wise people in the US were pushing the development of better fission bombs when the whole debate about hydrogen bombs was going on in the late 40s.

Some have also argued that it’s better to have big thermonuclear weapons rather than ’small’ fission weapons so that countries won’t actually feel tempted to use the small bombs with their smaller yields. But this argument crucially rests on quantitative aspects. A Hiroshima style bomb with a yield of 20 kT is as good as a 1 megaton hydrogen bomb when employed strategically in sufficient quantities. Hydrogen bombs are certainly not essential for deterrence; in fact what’s really essential is an efficient triumvirate of delivery systems (submarines + bombers + missiles). That is what India should focus on instead of getting too hung up over hydrogen bombs and bigger bangs.

Note: The analysis is of course not my own. Apart from the websites I have referred to the excellent and authoritative The Nuclear Express by Thomas Reed and Danny Stillman, both of whom are veteran nuclear weapons specalists.