Indian Defence Review

In the aftermath of the Democratic People’s Republic of Korea (DPRK) testing a “thermonuclear” weapon on 3 September 2017, the focus upon that country’s nuclear capability has been on the yield of the said test. Estimates for the yield vary widely – between 50 kilotons1 and 250 kilotons2 – reflecting the usual lack of consensus among seismologists in interpreting seismic data from suspected nuclear tests. Invariably, comparisons are likely to be made between North Korea’s undoubtedly powerful test and India’s proven nuclear capability to date.

One of those questions is likely to be whether India’s deterrent is “credible” given doubts that have been articulated by Dr. K. Santhanam about the test of a thermonuclear device in 1998. Santhanam has argued that the Shakti-1 device failed to achieve its designed yield and as such has to be considered a failure. That, in turn, means more tests are needed to establish India’s thermonuclear capability.3 It should be noted, however, that Santhanam’s claims were met with a detailed and rigorous rebuttal by Dr. R. Chidambaram and Dr. Anil Kakodkar.4 Kakodkar went even further and claimed, during the course of an interview with Karan Thapar, that India has produced and deployed several thermonuclear weapons:5

Karan Thapar: We have a credible thermonuclear bomb?

Anil Kakodkar: Why are you using singular? Make that plural.

Karan Thapar: So you are saying to me that we have thermonuclear bombs – in the plural?

Anil Kakodkar: Yes.

For the purposes of this article, it will be assumed that Kakodkar is being less than truthful and that India has not deployed any thermonuclear weapon. Two questions arise in this regard:

• Is India’s deterrent credible without thermonuclear weapons?
• Does India need thermonuclear weapons?

The answer to each of these questions is “yes” because, first, the credibility of India’s deterrent is independent of whether or not it has deployed thermonuclear weapons, and second, India’s deterrent, as it evolves, would benefit from the flexibility of design, weight and yield that thermonuclear weapons allow.

Credibility of the Deterrent

It is unfortunate that Santhanam, among others, has adopted the stance that the “failure” of the thermonuclear test in 1998 means that the Indian nuclear arsenal has been limited to fission weapons with an yield of 20 to 25 kilotons.6 This is patently untrue for, as was confirmed by Chidambaram and Kakodkar, the primary stage of the thermonuclear device was a fusion-boosted-fission device.7 Therefore, any discussion of India’s arsenal must perforce include fusion-boosted-fission weapons.

8 Outside of the United States, France deployed the 70-kiloton AN-22 fission bomb, which weighed a mere 700 kg, as well as the MR-31 fission warhead (mated with the S-2 Intermediate Range Ballistic Missiles), which too, while weighing 700 kg, had a yield of 120 kilotons.9

There is some anecdotal evidence for India developing fission weapons approaching these French weapons in terms of yield. Indications are that the first Indian nuclear weapons design had a mass of about 1000 kg with a yield of 12 to 15 kilotons. Subsequently, however, perhaps by 1982, when rumours of a fresh round of nuclear tests were in circulation, the said weapon had been scaled down to a more manageable mass of between 170 and 200 kg.10

It appears that a 100 kiloton fission weapon was later produced for aerial delivery with a mass of 200 to 300 kg.11 If this information is indeed accurate, it would mean that India had perfected a relatively high-yield fission weapon with a relatively low mass for its class. One would expect that missile warheads of similar designs and yields would be feasible.12 

Given, however, doubts regarding whether fusion boosting actually increased the yield, it is unclear whether Orange Herald should be referred to as the largest fission bomb tested or the largest fusion-boosted-fission tested.13 

France had greater success with deploying fusion-boosted-fission weapons with the 700 kg, 500 kiloton, MR-41 warhead, which armed the M1 and M2 Submarine-Launched Ballistic Missiles (SLBMs).14

A possible confirmation of India deploying the fusion-boosted-fission weapons might be found in the following sentence written by Admiral Arun Prakash in 2009 (at the height of the controversy generated by Santhanam’s statements questioning the success of the 1998 thermonuclear test):15

“In the midst of the current brouhaha, we need to retain clarity on one issue; given that deuterium tritium boosted-fission weapons can generate yields of 200-500 kt, the credibility of India’s nuclear deterrent is not in the slightest doubt.”

An even more potentially revealing comment was made in 2011 by Dr. Avinash Chander to theBusiness Standard. He said:16

“Now we talk of [accuracy of] a few hundred metres. That allows a smaller warhead, perhaps 150-250 kilotons, to cause substantial damage.”

To discount these statements – one by a former Chairman, Chiefs of Staff Committee and the other by a former Director-General of DRDO – would be folly, to say the least. To these must be added Kakodkar’s consistent assertions that India can field weapons up to a yield of 200 kilotons.17

It should be noted that even a prominent sceptic like Dr. Bharat Karnad acknowledges that India’s boosted-fission capability is significantly more reliable than its thermonuclear capability.18,19 

However, given that India’s 15 to 20 kiloton fission warheads and the 100 kiloton fission weapon developed in the 1980s weighed between 170 and 300 kg, it is somewhat surprising to see a claim that the Agni-I with a payload of 1000 kg would have a warhead with a yield of 20 to 30 kilotons.20

In other words, it is possible that the warhead of Agni-I may have a significantly higher yield than the 20 to 30 kilotons claimed by Karnad.

From a perspective of nuclear yield, it can therefore be argued that India’s needs are adequately met by tested and reliable fission and fusion-boosted-fission designs which can be scaled to meet the varying yield requirements up to a certain magnitude. In this regard, at least, the credibility of India’s deterrent does not require thermonuclear weapons.

Does India need Thermonuclear Weapons?

Despite the credibility of the Indian deterrent being unaffected by a fully proven thermonuclear capability, it is submitted that the development of thermonuclear weapons is an essential part of weapons development and that it will also make the deterrent more flexible.

Thermonuclear weapons need not have higher yields than either fission or boosted-fission weapons. For instance, the French TN-75 fitted to the M45 SLBM has a yield of only 100 kilotons. But they are inevitably lighter, with the 300 kiloton TN-80/81 warhead of the ASMP missile weighing a mere 200 kg.21 These lightweight, but relatively high-yield, warheads would enhance the potential efficacy of any Indian strike, particularly in respect of stand-off air-delivered munitions where the payload/yield trade-off has a direct bearing on the performance of an air-delivered missile.

Thermonuclear weapons achieve this superior weight to yield ratio by virtue of requiring less fissile material. This point is important for India since its reported fissile material stocks of weapons-grade plutonium and highly enriched uranium are relatively modest.22 Given that the Mk. 18 weapon used some 60 kg of HEU, and the Orange Herald device used 117 kg of HEU, it can be seen that large yield fission weapons use a considerable quantity of fissile material.23Thermonuclear weapons requiring only the critical mass necessary for a fission trigger, offer the prospect of making more efficient use of India’s fissile material stocks.

Thermonuclear weapons also offer the prospect of variable yield weapons. Indeed, shortly after the 1998 tests, Dr. Frank Barnaby suggested that an operational nuclear weapon could have variable yields of 5, 50 and 500 kilotons.24 Such flexibility obviates the need for India to maintain a separate inventory of fission weapons to provide lower-yield options alongside larger fusion-boosted-fission weapons. This would inevitably make fusion weapons a potentially cost-effective option.

Furthermore, if India is considering multiple warheads for missiles – the purported Agni-VI for example – then the lower weight of thermonuclear weapons would be essential for this purpose.25Thus, the French M4A and M4B SLBMs housed six TN70/71 warheads. While each warhead had an yield of 150 kilotons, the TN70 weighed less than 200 kg and the TN71 less than 175 kg.26 Britain has also followed this model for the Trident D-5 SLBM force.27 In contrast, fusion-boosted-fission weapons of similar yields will, as shown earlier, weigh some 700 kg, making them unsuitable for multiple warhead purposes.

Conclusion

India has not defined its deterrent requirements in either quantitative or qualitative terms. Inferences are drawn from the text of its nuclear doctrine and based on the possible targets in the territories of its rivals and adversaries. While thermonuclear weapons are not necessary for maintaining a credible deterrent, they serve the purpose of enabling India to make effective use of its relatively limited fissile material stockpile. Since India’s deterrent requirements will evolve with time, it behoves a country with limited resources to maintain as flexible a deterrent as possible. To this end, thermonuclear weapons, offering variable yields and light-weight warheads that use less fissile material, should be an essential component in India’s arsenal.

Courtesy: http://www.idsa.in/idsacomments/does-india-need-thermonuclear-weapons_sbmaharaj_220817