China, India and possibly Pakistan intend to deploy nuclear weapons at sea. Ultimately, such deployments may well have a stabilising effect — that is, they may reduce the risk of full-scale war and nuclear use. Sea-based nuclear weapons might, for instance, fit well with 'no-first-use' doctrines.
They might also encourage reduced investment in more destabilising forces such as weapons fired from fixed sites, which are vulnerable and thus suited to a 'first strike'. And after all, sea-based nuclear weapons were widely seen as stabilising during the Cold War.
However, we should beware of applying simple retrospective visions of the US-Soviet balance to the Asian strategic scene. There are various reasons to doubt that deployment of sea-based nuclear weapons in Indo-Pacific Asia will be stabilising.
First, to state the obvious, there are three independent centres of nuclear power in Asia: China, India and Pakistan. And that is before counting the US and Russia, as well as North Korea, which one day could also want to base some of its weapons at sea. This fundamental element of the Asian nuclear scene will remain regardless of where weapons are based.
Second, although wanting the permanent presence of nuclear weapons at sea as a second-strike capability to guarantee their survival is arguably a stabilising factor, that may not be the driving motivation of all three countries. There seems to be strong interest in China and India, at least, in the symbolic value of strategic submarines, including for parochial or bureaucratic reasons. In addition, these two countries may prefer to avoid deploying nuclear-armed sea-launched ballistic missiles, in order to maximise political control over the weapons. It should also be added, regarding China, that the choice of a secure SSBN base on Hainan island, where berths are largely immune to a first strike, puts less pressure on Beijing to adopt a practice of continuous at-sea deterrence.
Third, deployment of nuclear weapons at sea in Indo-Pacific Asia does not only mean strategic missiles based on submarines.
It may include cruise missiles on vulnerable surface platforms. It will also probably include theatre systems designed to target naval forces, notably by Pakistan. This would not be a stabilising factor if command-and-control dilemmas for such systems are resolved in a way that dilutes the ability of national authorities to maintain the highest degree of political control over the weapons at all times. It should be remembered that probably the closest call for the use of nuclear weapons since 1945 concerned naval theatre weapons: it was in Cuba in October 1962.
Fourth, Indo-Pacific waters lend themselves less easily to the deployment of non-detectable submarines than was the case for the Cold War confrontation, when the Atlantic and the Pacific oceans offered more opportunities. This is especially true since India and Pakistan are likely to field only medium-range systems for some time, forcing their submarines to operate relatively close to the adversary's shores. It is also worth mentioning that unlikely accidents can happen, as was the case in 2009 when British and French SSBNs collided, and it took them a while to realise what had happened.
More generally, the transition period towards the deployment of operational SSBNs by China, India and Pakistan is likely to be long, tortuous and dangerous, for technical and budgetary reasons. What happens if one (or two) of the three countries manages to have a secure sea-based second-strike capability well before the others?
Simply put, it is impossible to argue that the deployment of sea-based nuclear weapons in Indo-Pacific Asia will be inherently stabilising.