Unable to match India's massive military expenditures, Pakistan has taken an asymmetric approach to compensate for its comparative weakness: Building up its nuclear arsenal. In fact, Islamabad has already begun to design and develop tactical nuclear weapons that could someday be deployed against Indian troops on the battlefield. Now Pakistan is searching for the second-strike capability — the means of threatening nuclear retaliation even after having suffered an overwhelming nuclear strike. The Babur-3 submarine-launched cruise missile might provide this. With a reported range of 450 kilometers (280 miles), the missile would be able to reach most of India's major cities, though much of the country's interior — including the capital of New Delhi — would still be beyond the reach of Pakistan's nascent at-sea nuclear delivery program.
Pakistan has its reasons for pursuing such capabilities. For one, India is ramping up its investment in anti-ballistic missile defense systems. This, in turn, has prompted Pakistan to shift its attention to producing cruise missiles as an alternative delivery method to ballistic missiles.
India has also begun to develop its own sea-based nuclear deterrent. Based primarily on submarine-launched ballistic missiles, this deterrent would make India's second-strike measures far more credible, pressuring Pakistan to respond in kind by boosting its second-strike capabilities to better discourage a nuclear attack. This objective has become all the more important to Islamabad, since its introduction of tactical nuclear weapons has lowered the threshold for the use of nuclear weapons in the region.
Still, creating a plausible sea-based second-strike threat requires a submarine fleet that can fire missiles. As of now Pakistan has only five of these vessels, three of which could be considered fairly modern. Nevertheless, Islamabad plans to dramatically expand its submarine fleet: In 2015, it struck a deal with Beijing to buy eight submarines similar to the Yuan-class model. Pakistan is also in the process of moving its main submarine base from Karachi to Ormara. (The former is more vulnerable to attack because of its proximity to the Indian border.)
When all is said and done, though, Pakistan's decision to rely on nuclear weapons as a means of warding off attack from a more powerful India has increased the chance of nuclear warfare breaking out in South Asia. Though Islamabad's quest for a sea-based nuclear deterrent is hardly surprising, it is a conspicuous example of an alarming pattern of posturing between two nuclear powers that have a long and volatile history of hostility toward each other.