The Indian Navy has given special attention to the modernization of its submarine fleet. In this regard, one such key initiative is the S5-class nuclear-powered ballistic missile submarines (SSBN). The initial plan was to build six submarines, but reports from India indicate that four will be built. India is eager to induct these submarines sooner for their operational advantages and because it needs to retire INS Arihant soon, which was intended as a technology demonstrator rather than an active deterrent. Some would argue that the Indian SSBNs will counter the Chinese threat, but given the recent Indo-Pak 2025 crisis, and the INS Arihant’s active deployment in the 2019 Pulwama crisis. Therefore, the new SSBN program will not stabilize the region but further fuel instability by expanding the asymmetry in the region.
Like the Arihant class SSBN project, the details regarding the S5-class are also shrouded in secrecy. As per the media reports, the newer SSBNs are expected to double the displacement of the Arihant class. This puts the submarine displacement at around 13,000 tons. The S5 submarine is expected to have 16 missile tubes. This is double compared to the S4 Arihant-class SSBN (INS Ardhiman), which is undergoing sea trials, and only has eight tubes. This is a significant increase in missile tubes from the earlier operational Arihant-class submarines, INS Arihant and INS Arighat, which only have four missile tubes each.
The Times of India reported on September 22, 2025, citing an unnamed Indian scientist involved with the S5 SSBN project, that the new SSBNs will feature larger 200 MW reactors, compared to the 83 MW reactors used in Arihant-class SSBNs. The reactor, currently under development at Bhabha Atomic Research Centre (BARC), will double the endurance levels of the S5-class submarines. This is a significant milestone, as The Hindu reported that the Arihant-class submarine reactor’s limited fuel inventory prevents extended deployments far from Indian shores, as it would require frequent, time-consuming refueling. In contrast, the S5 subs will be refueled only once after ten years of active deployment. Thus, the new reactor will enhance the S5 submarine’s operational readiness by reducing the need for frequent and complex refueling, allowing the vessel to stay at sea longer and spend less time in port.
India is developing long-range submarine-launched missiles (SLBMs) for the S5-class, including the newer and more advanced K5 and K6 missiles. According to some sources, the missile range is 5,000 to 6,000 km, while some claim it can reach targets exceeding 8,000 km. In March 2025, the Defence Research and Development Organisation (DRDO) publicly revealed the K5 missile storage canister, which indicates that the missile has now entered the tangible assembly phase from the design phase. In addition, a report in May 2025 claimed that the development work on the K5 SLBM had been completed. This indicates that the test trials of K5 are expected sooner rather than later. This seems possible because India intends to integrate this missile with the Arihant-class last boat, S4*. On the other hand, the K6 is an SLBM that can engage its targets up to 8,000 km. K6 will also be integrated with Multiple Independently Targetable Re-entry Vehicle (MIRV) technology, allowing India to add more firepower to its S5-class SSBNs. The missile has a reported speed of up to Mach 7.5; however, it could be higher.
Given the rate at which the Indian domestic shipbuilding industry is delivering naval vessels to the Indian Navy, the SSBNs are expected to be built, launched, and commissioned into service in less time than it took for Arihant-class SSBNs. The work has recently been accelerated to construct the next-generation S5-class SSBNs. This is evident from establishing a new 600 m facility capable of building SSBNs near Cochin Shipyard in Kerala, besides the Shipbuilding Center (SBC) located at Vishakhapatnam. This will enable the rapid construction of submarines at two facilities. All these efforts are part of the plan to construct SSBNs by 2027.
In addition, this modernization drive also sheds light on India’s potential plan to increase its nuclear warhead production, as advocated by the Indian scholar Bharat Karnad last year, who argued that the current number of warheads is inadequate, as India has entered the MIRV era. If one looks at Indian warhead production in the last ten years, it has increased at a gradual pace from 118 in 2015 to 180 in 2025. However, in that era, India did not induct any MIRV missile. With the future induction of land-based Agni-V MIRV variant, and the deployment of K-6 MIRV-capable SLBM onboard four S5 SSBNs, the annual warhead production will likely increase.
The S5-class will be quieter, with more payload, enhanced endurance, extended mission deployment, advanced onboard sensors, and less fuel replenishment, making it a potent platform. The desire to build S5 reflects New Delhi’s strategy to retain an operational advantage vis-à-vis Pakistan and China. However, India’s obsession with Pakistan, which is exemplified by its belligerent launch of preemptive strikes in 2019 and 2025, indicates that the newer submarines will pose more of a threat to Pakistan than to China. Considering the current Arhinat-class and future S5-class SSBNs, the asymmetry between Pakistan and India’s sea-based nuclear forces will increase.
To counter this emerging threat, Pakistan can take specific practical initiatives in the short and medium term. As a stopgap arrangement, Pakistan can launch Intelligence Surveillance and reconnaissance (ISR) satellites and induct a modest fleet of long-range maritime fixed-wing manned and unmanned systems capable of extended endurance. These systems will help detect, track, and hunt India’s SSBNs. In the medium to long run, although it seems costly and challenging, Pakistan has to build its own SSBNs to provide the country with assured second-strike capability to keep the balance in the Indian Ocean Region in order.
Author: Usman Haider has an MPhil degree in Strategic Studies from the National Defense University, Islamabad, Pakistan. His articles have been published in The Diplomat, Australian Institute of Affairs, South Asian Voices, South China Morning Post, Real Clear Defense, and many others.
