The danger of sea-based nuclear weapons in Asia depends on the strategic context of the potential protagonists, along with the particulars of the platforms, delivery system, and doctrines.

Perhaps the least menacing in the short term is the interaction between India and China as each builds its sea-based nuclear capability. There are still years to go before each state has systems coupled with the need to deploy them in locations that could lead to dangerous interactions.

A second dyad, between US sea-based nuclear weapons and the growing Chinese maritime nuclear arsenal, has the potential for misunderstanding, risk-taking, and escalation, but Washington and Beijing are not in a state of on-again, off-again militarised hostilities. This, coupled with the distance from China that US nuclear-armed ballistic missile submarines are likely patrol, limits some potentially dangerous interactions.

The India-Pakistan dyad, however, carries the potential to be the most menacing in the short-to-medium term.

Both India and Pakistan are at the initial stages of deploying nuclear weapons on submarines. Being new to a deployed technology and operational technique does not mean the two governments and their militaries will not be careful or capable. Both states are likely to be highly cautious and professional in their deployment of these capabilities. However, there is always a learning curve with new capabilities and therefore always chances for misperception, miscalculation, and the threat of escalation.

Three additional factors in the South Asian context make this newly emerging set of capabilities particularly troubling.

The first is the very short range of India's first generation submarine-launched ballistic missile (the K-15 has a reported range of 750km) and Pakistan's likely submarine-launched cruise missile (the Babur, with a reported range of 700km). The second is that it appears Pakistan will be deploying its sea-based nuclear capability in a dual-use platform, a diesel-powered attack submarine. Finally, the two states have a history of wars and militarised crises over a range of disputes that will not be resolved anytime soon. 

Unlike the deployment of nuclear warheads on land-based missiles or nuclear gravity bombs, sea-basing of nuclear weapons carries a much greater chance of close-up and regular interaction between the forces of two potential protagonists. In peacetime, once India and Pakistan actually have operational platforms deployed, it can be expected that each side will seek to gather intelligence on the acoustic signature of the other side's submarines, along with information about operating patterns and locations. This creates chances for accidents, incidents, or heightened tensions, particularly as the relatively short ranges of the missiles mean that deployment areas may be relatively close to the other's territorial waters.

Yes, such submarine-versus-submarine interactions occur already without any public acknowledgment of increased tensions, but the importance of nuclear weapons may cause both sides to take greater risks both to gather intelligence and to defend a nuclear-armed platform. Similarly, both sides may become more aggressive in patrolling and defending territorial waters, contiguous zones, and even exclusive economic zones if they want to deny the other side from gaining operational familiarity with a particular stretch of water.

If another militarised crisis between India and Pakistan were to occur after the deployment of sea-based nuclear weapons, the chances of inadvertent escalation will be higher than in an environment absent these platforms. In the case of Pakistan's likely nuclear platform – an Agosta-class submarine basically indistinguishable from its conventionally-armed counterpart – Indian naval commanders and their civilian leadership may be faced with a difficult dilemma. Protecting India's surface and submarine fleet from Pakistan's submarines in a crisis or war requires aggressive detection measures and attacking potential contacts. However, India may feel constrained if it does not want to inadvertently escalate a crisis or conflict by destroying the 'secure second-strike' portion of Pakistan's nuclear triad. If India were to destroy a Pakistani submarine carrying nuclear-armed missiles as part of a conventional war, would Pakistan's leadership interpret this action as crossing a nuclear threshold?

Similarly, in a future crisis or conventional war, what would Pakistan do to place itself in a better position to track and, if possible, destroy the INS Arihant or its successors? Pakistan has shown itself both willing and able, as far back as 1971, to undertake long-range, risky submarine operations in an attempt to strike at high-value Indian assets on India's east coast. Would India view such a Pakistani operation in a future crisis as escalatory? What would its response be?

The Lowy Institute gratefully acknowledges support from the John D and Catherine T MacArthur Foundation for this Interpreter debate, which is part of a broader research, dialogue and outreach project on strategic stability in Indo-Pacific Asia