India’s naval forces are advancing a sweeping effort to standardise and integrate the design of their future underwater combat fleet, marking one of the most ambitious submarine modernisation programmes in the country’s history. The initiative centres on harmonising two major submarine lines—Project-77 nuclear-powered attack submarines (SSNs) and Project-76 next-generation conventional submarines (SSKs)—through a shared technological backbone of sensors, combat systems, and mission architecture.
Defence planners describe the approach as a structural shift toward a “National Submarine” framework, designed to ensure interoperability, reduce lifecycle costs, strengthen domestic production capacity, and simplify crew training across platforms that have traditionally been developed in isolation.
At its core, the programme aims to eliminate fragmentation in India’s underwater fleet, which has historically relied on a mix of imported submarine classes, each equipped with proprietary combat systems, maintenance pipelines, and supplier ecosystems. The new doctrine instead prioritises modularity, interchangeability, and indigenous control of critical subsystems.
The centrepiece of this transformation is a domestically developed Combat Management System (CMS) that will be installed across both Project-76 and Project-77 platforms. This system is intended to function as the operational “brain” of the submarine fleet, integrating all battlefield inputs and command decisions into a unified digital environment.
According to defence sources, the CMS will feature a modular architecture capable of handling sensor fusion, fire-control solutions, navigation, and tactical engagement management in real time. It will be designed to process data from sonar arrays, electronic support measures, periscopes, and communication intercepts, producing a consolidated situational awareness picture for commanders.
Standardisation extends beyond software. Identical multi-function displays and operator consoles will be deployed across both submarine classes, allowing naval personnel to transition between nuclear and conventional boats with minimal retraining. This design philosophy is expected to significantly streamline manpower planning and reduce training overheads.
A major technological shift under the programme involves the replacement of traditional optical periscopes with advanced non-penetrating optronic masts. These systems, developed by the Instruments Research and Development Establishment IRDE, will eliminate the need for physical hull-penetrating periscopes and instead rely on electronically transmitted imagery.
The optronic masts will provide high-definition visual, infrared, and thermal imaging capabilities, feeding encrypted data directly into the CMS via fiber-optic networks. This enables faster reaction cycles and reduces the risk of detection, as the submarine no longer requires a rigid periscope assembly protruding above the hull.
Alongside visual sensors, both submarine classes will incorporate standardised electronic warfare suites, communication masts, and Electronic Support Measures (ESM) systems. This convergence is intended to ensure a uniform baseline for signal intelligence and threat detection across the fleet.
Underwater acoustic detection will be governed by a shared Integrated Sonar System (ISS) developed by the Naval Physical and Oceanographic Laboratory NPOL. The system will combine bow-mounted, flank, and towed-array sonar configurations with passive intercept capabilities, enabling multi-directional detection of hostile platforms in complex maritime environments.
The offensive architecture of both submarine classes is being aligned to ensure compatibility across torpedoes, missiles, and future long-range strike systems. Both Project-76 and Project-77 platforms will deploy the domestically developed Varunastra heavyweight torpedo, alongside the next-generation Takshak torpedo currently under development.
Beyond conventional torpedo warfare, open-source defence assessments suggest that the larger Project-77 SSNs will feature a 24-cell Vertical Launch System (VLS). This configuration is expected to support a range of long-range precision strike weapons, including land-attack cruise missiles and future hypersonic systems.
Systems such as the Nirbhay cruise missile and emerging navalised hypersonic platforms linked to BrahMos Aerospace BrahMos Aerospace are expected to be integrated into the shared launch architecture. While Project-76 submarines are smaller and do not include large VLS modules, they are being designed with flexible launch interfaces that could allow missile deployment through torpedo tubes or modular external launch systems.
Officials indicate that the goal is to ensure near-identical digital fire-control interfaces across both submarine types. This would allow crews to operate different weapon systems without needing to learn entirely separate engagement procedures.
Despite the push for commonality, the two submarine classes will retain fundamentally different propulsion systems. Project-77 nuclear attack submarines will be powered by a compact 190-megawatt light-water reactor, enabling virtually unlimited endurance and sustained high-speed submerged operations.
In contrast, Project-76 conventional submarines will rely on diesel-electric propulsion systems enhanced by lithium-ion batteries and Air Independent Propulsion (AIP) modules. This combination is designed to extend underwater endurance significantly compared to traditional diesel-electric boats.
However, naval engineers are reportedly exploring a shared pump-jet propulsion architecture across both platforms. Pump-jets are known to reduce cavitation and hydrodynamic noise compared to conventional propellers, offering a substantial stealth advantage—particularly in contested acoustic environments where detection sensitivity is high.
To further reduce acoustic signatures, both submarine classes will be coated with advanced anechoic tiles manufactured domestically. These rubberised coatings absorb sonar waves and dampen internal machinery vibrations, making the vessels harder to detect.
A critical component of the programme is the expansion of domestic industrial capability. Both submarine classes will be constructed using high-tensile steel such as HY-130-grade alloys produced by Mishra Dhatu Nigam MIDHANI. These materials are engineered to withstand extreme underwater pressure while maintaining structural resilience and acoustic dampening characteristics.
Defence planners view this material standardisation as essential for reducing dependency on foreign suppliers for hull construction and key structural components. It also allows for economies of scale across multiple submarine production lines, potentially reducing long-term procurement costs.
Military officials describe the overarching strategy as an effort to avoid what is informally referred to as the “technology fragmentation trap”—a situation where multiple submarine classes rely on incompatible systems, leading to logistical complexity, high maintenance costs, and dependency on foreign vendors for critical upgrades.
By enforcing a shared technological baseline across nuclear and conventional submarines, India aims to create a cohesive underwater warfare ecosystem where sensors, weapons, software, and training systems are largely interchangeable.
This approach is also expected to enhance operational readiness. In a standardised fleet, spare parts inventory becomes more predictable, software upgrades can be deployed uniformly, and personnel can be reassigned between platforms without extensive retraining cycles.
The Project-76 and Project-77 convergence is the emergence of what defence analysts describe as a “National Submarine” doctrine. Under this model, submarine design is no longer treated as a series of isolated procurement programmes but as a unified technological ecosystem governed by shared standards.
The architecture would represent a significant departure from India’s historical reliance on diverse imported submarine classes, each with distinct operational frameworks. Instead, the future fleet would function as an integrated underwater force built around indigenous digital systems and standardised engineering principles.
