India may be reinterpreting its nuclear weapons doctrine, circumstantial evidence suggests, with potentially significant ramifications for the already tenuous nuclear balance in South Asia.

New assessments suggest that India is considering allowing for pre-emptive nuclear strikes against Pakistan’s arsenal in the event of a war. This would not formally change India’s nuclear doctrine, which bars it from launching a first strike, but would loosen its interpretation to deem pre-emptive strikes as defensive.

It would also change India’s likely targets, in the event of a war, to make a nuclear exchange more winnable and, therefore, more thinkable.

Analysts’ assessments, based on recent statements by senior Indian officials, are necessarily speculative. States with nuclear weapons often leave ambiguity in their doctrines to prevent adversaries from exploiting gaps in their proscriptions and to preserve flexibility. But signs of a strategic adjustment in India are mounting.

This comes against a backdrop of long-simmering tensions between India and Pakistan — including over state-sponsored terrorism and the disputed territory of Jammu and Kashmir — which have already led to several wars, the most recent in 1999.

The new interpretation would be a significant shift in India’s posture that could have far-reaching implications in the region, even if war never comes. Pakistan could feel compelled to expand its arsenal to better survive a pre-emptive strike, in turn setting off an Indian buildup.

This would be more than an arms race, said Vipin Narang, a Massachusetts Institute of Technology professor who studies nuclear powers.

“It’s very scary because all the ‘first-strike instability’ stuff is real,” Mr. Narang said, referring to a dynamic in which two nuclear adversaries both perceive a strong incentive to use their warheads first in a war. This is thought to make nuclear conflict more likely.

Hidden in Plain Sight

Hints of a high-level Indian debate over the nuclear doctrine mounted with a recent memoir by Shivshankar Menon, India’s national security adviser from 2011 to 2014.

“There is a potential gray area as to when India would use nuclear weapons first” against a nuclear-armed adversary, Mr. Menon wrote.

India, he added, “might find it useful to strike first” against an adversary that appeared poised to launch or that “had declared it would certainly use its weapons” — most likely a veiled reference to Pakistan.

Mr. Narang presented the quotations, along with his interpretation, in Washington last week, during a major nuclear policy conference hosted by the Carnegie Endowment for International Peace.

“There is increasing evidence that India will not allow Pakistan to go first,” he told a gathering of international government officials and policy experts.

Mr. Menon’s book, he said, “clearly carves out an exception for pre-emptive Indian first use in the very scenario that is most likely to occur in South Asia.”

The passage alone does not prove a policy shift. But in context alongside other developments, it suggests either that India has quietly widened its strategic options or that officials are hoping to stir up just enough ambiguity to deter its adversaries.

After Mr. Narang’s presentation generated attention in the South Asian news media, Mr. Menon told an Indian columnist, “India’s nuclear doctrine has far greater flexibility than it gets credit for.”

Mr. Menon declined an interview request for this article. When told what the article would say, he did not challenge its assertions. India’s Foreign Ministry did not respond to a request for comment.

Whether these signals indicate a real shift or a strategic feint, analysts believe they are intended to right a strategic imbalance that has been growing for almost a decade.

The Pakistan Problem

Should India sustain a nuclear attack, its doctrine calls for a major retaliation, most likely by targeting its adversary’s cities. When this policy was announced in 2003, it fit the threat posed by Pakistan’s arsenal of long-range, city-destroying weapons.

Since then, Pakistan has developed smaller warheads designed for battlefield use. These were meant to address Pakistan’s India problem: The Indian military is much larger, virtually ensuring its victory in an all-out war.

Such weapons could be used against invading Indian troops, halting a war before it could be lost. This would exploit a gap in India’s doctrine: It is hard to imagine that India would escalate to total nuclear war, as its doctrine commands, over a small battlefield strike on Pakistani soil.

This created a Pakistan problem for India: Its chief adversary had made low-level nuclear war thinkable, even potentially winnable. Since then, there have been growing hints of debate over modifying the Indian doctrine.

B. S. Nagal, a lieutenant general who led India’s nuclear command from 2008 to 2011, argued in a 2014 article for a policy of “ambiguity” as to whether India would launch a pre-emptive nuclear strike.

Also that year, the Bharatiya Janata Party said it would consider changing India’s doctrine, but then abandoned this position. It took power in national elections a few weeks later.

Last November, Manohar Parrikar, then the defense minister, said India’s prohibition against nuclear first use was too restrictive, though he added that this was only his opinion.

Another reason analysts suspect change: India’s doctrine initially served to persuade the United States to drop economic sanctions it had imposed over nuclear tests. Given President Trump’s softer stance on proliferation, that impetus may no longer apply.

‘The Seductive Logic’

Mr. Menon, in his book, seemed to settle on an answer to India’s quandary: “Pakistani tactical nuclear weapon use would effectively free India to undertake a comprehensive first strike against Pakistan,” he wrote.

The word “comprehensive” refers to a nuclear attack against an adversary’s arsenal, rather than its cities. It is meant to instigate and quickly win a nuclear exchange, leaving the other side disarmed.

Taken with a policy of pre-emption, these two shifts would seem to address India’s Pakistan problem, in theory persuading Pakistani leaders that a limited nuclear war would be too dangerous to pursue.

For India, Mr. Narang said, “you can really see the seductive logic” to such an approach. This would be “really the only pathway you have if you’re going to have a credible nuclear deterrence.”

It is impossible to know whether statements like Mr. Menon’s are intended to quietly reveal a policy shift, while avoiding the crisis that would be set off by a formal change, or merely stir doubt.

Either way, the intent appears the same: to create just enough uncertainty in the minds of Pakistani leaders that they become restrained by the potential threat of pre-emptive Indian strikes.

But if that threat is plausible, then the distinction between a real threat and a feint blurs.

Use It or Lose It

Shashank Joshi, a fellow at the Royal United Services Institute, said he suspected that Mr. Menon was signaling something subtler: a warning that India’s strategy could adapt in wartime, potentially to include first strikes.

That distinction may be important to Indian officials, but it could be lost on Pakistani war planners who have to consider all scenarios.
Mr. Joshi, in a policy brief for the Lowy Institute, an Australian think tank, tried to project what would happen if India embraced such a policy, or if Pakistan concluded that it had.

First would come the arms race.

The fear of a first strike, Mr. Joshi wrote, “incentivizes Pakistan to undertake a massive nuclear buildup, in order to dispel any possibility of India disarming it entirely.”

India, whatever its strategy, would feel compelled to keep pace.

Second comes the tightening of nuclear tripwires, Mr. Joshi warned, as “this reciprocal fear of first use could pull each side in the direction of placing nuclear forces on hair-trigger alert.”

Finally, in any major armed crisis, the logic of a first strike would pull both sides toward nuclear escalation.

“If Pakistan thinks India will move quickly, Pakistan has an incentive to go even quicker, and to escalate straight to the use of the longer-range weapons,” Mr. Joshi wrote.

This thinking would apply to India as well, creating a situation in which the nuclear arsenal becomes, as analysts dryly put it, “use it or lose it.”

‘That Can Blow Back Real Quick’

The most optimistic scenario would lock South Asia in a state of mutually assured destruction, like that of the Cold War, in which armed conflict would so reliably escalate to nuclear devastation that both sides would deem war unthinkable.

This would be of global concern. A 2008 study found that, although India and Pakistan have relatively small arsenals, a full nuclear exchange would push a layer of hot, black smoke into the atmosphere.

This would produce what some researchers call without hyperbole “a decade without summer.” As crops failed worldwide, the resulting global famine would kill a billion people, the study estimated.

But nuclear analysts worry that South Asia’s dynamics would make any state of mutually assured destruction less stable than that of the Cold War.

For one thing, Pakistani leaders view even conventional war with India as an existential threat, making them more willing to accept nuclear risks.

For another, a large-scale terrorist attack in India could be perceived, rightly or wrongly, as Pakistan-sponsored, potentially inciting war. The

disputed territory of Jammu and Kashmir, where conflict sometimes boils over, adds a troubling layer of volatility.

“Maybe it is this Reaganesque strategy,” Mr. Narang said, comparing India’s potential strategic shift to President Ronald Reagan’s arms race with the Soviet Union. “But Pakistan has a much bigger security problem than the Soviet Union did. And that can blow back real quick.”