Nilgiri, Sandhayak and Arnala Classes: India's Indigenous Naval Shipbuilding Triad
A recent report highlighted the Nilgiri, Sandhayak and Arnala classes of warships as representing three distinct pillars of India's naval combat capability: frontline surface combat, hydrographic survey, and coastal anti-submarine warfare.
The Nilgiri class (Project 17A) comprises stealth guided-missile frigates built to succeed the older Shivalik-class (Project 17) frigates.
The Sandhayak class consists of large hydrographic survey vessels tasked with mapping the seabed and generating navigational charts.
The Arnala class consists of shallow-water anti-submarine warfare (ASW) craft designed for coastal underwater surveillance and mine-laying support.
All three classes are designed by the Indian Navy's in-house Warship Design Bureau and built at domestic shipyards, reflecting the indigenous shipbuilding push under the Aatmanirbhar Bharat framework.
Project 17A: Nilgiri-Class Stealth Frigates
Project 17A is the Indian Navy's follow-on programme to Project 17 (Shivalik class), producing seven stealth guided-missile frigates with reduced radar, thermal and acoustic signatures. The class is being built jointly by Mazagon Dock Shipbuilders Limited (MDL), Mumbai and Garden Reach Shipbuilders & Engineers (GRSE), Kolkata, split four ships to MDL and three to GRSE.
The Nilgiri class represents the Navy's principal indigenous frontline surface combatant, replacing an earlier generation of imported/part-imported frigate designs and demonstrating the maturity of India's warship design and construction ecosystem.
Sandhayak-Class Survey Vessels (Large)
The Sandhayak class is a four-ship series of Survey Vessel (Large) — SVL — built to replace the Navy's earlier hydrographic survey fleet. These vessels conduct coastal and deep-water hydrographic surveys, oceanographic data collection, and search-and-rescue operations, and are essential to producing the nautical charts used for safe navigation and maritime boundary delimitation.
Key Details
- Approximately 110 metres in length; the class comprises INS Sandhayak, INS Nirdeshak, INS Ikshak and INS Sanshodhak.
- Equipped with autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs) for seabed mapping.
- Designed by the Warship Design Bureau and built domestically, continuing the Navy's self-reliance in specialised, non-combatant vessel classes.
Hydrographic survey capability underpins India's maritime domain awareness, EEZ (Exclusive Economic Zone) charting, and support to both naval operations and commercial shipping — a "force multiplier" role distinct from combat frigates.
Arnala-Class Anti-Submarine Warfare Shallow Water Craft
The Arnala class is a series of shallow-water ASW craft intended to replace the ageing Abhay-class corvettes, filling the gap in littoral (coastal) anti-submarine and anti-mine warfare that larger frigates and destroyers are not optimised for.
Key Details
- Approximately 77–78 metres in length, displacing around 900 tonnes; propelled by waterjets for shallow-water manoeuvrability.
- Equipped with lightweight torpedoes, rocket launchers, mines, naval guns, and shallow-water sonar; capable of surveillance and search-and-attack missions up to 200 nautical miles from shore.
- Lead ship INS Arnala; designed for low-intensity maritime operations, coastal ASW, and mine warfare — roles critical to countering sub-surface threats near India's coastline.
Coastal ASW craft such as the Arnala class address a distinct internal/coastal security requirement — detecting and neutralising submarine or underwater threats close to shore, complementing the blue-water role of Nilgiri-class frigates.
- Nilgiri class (Project 17A): 7 ships planned; ~6,670 tonnes displacement; ~149 m length; over 75% indigenous content.
- Sandhayak class: 4 survey vessels; ~110 m length.
- Arnala class: shallow-water ASW craft; ~900 tonnes displacement; ~77–78 m length; operational range up to 200 nautical miles from shore.
- All three classes are designed by the Indian Navy's Warship Design Bureau and built at Indian shipyards (including Mazagon Dock and GRSE), reflecting the indigenous defence shipbuilding programme.