Backgrounder: Nilgiri, Sandhayak and Arnala naval classes

Nilgiri, Sandhayak and Arnala naval classes: what happened?

India’s Navy must guard a long coast, a large Exclusive Economic Zone and sea lanes that carry most of the country’s trade by volume. One ship type cannot do it all. Frigates fight on the surface, survey ships map the seabed, and small ASW craft hunt submarines close to shore. These three classes are that layered design, built in India.

• Coastline about 11,098 km; EEZ nearly 2.4 million square kilometres; sea lanes carry close to 90% of India’s trade by volume.
• Project 17A: seven Nilgiri-class frigates; MDL Mumbai builds four, GRSE Kolkata three; latest are INS Dunagiri (fifth) and INS Mahendragiri.
• Sandhayak-class: four ships; INS Sanshodhak is the fourth and final.
• Arnala-class: eight ships with GRSE and L&T Shipbuilding; INS Agray is the fourth; a parallel Mahe-class at Cochin Shipyard lifts planned ASW shallow water craft to 16.
• Indigenous content: 75% for Project 17A frigates; over 80% for Sandhayak survey vessels. Across the Navy, 64 of 66 ships and submarines on order are being built in India.

What does each class do?

• Nilgiri-class (Project 17A): multi-mission stealth frigates for anti-air, anti-surface and anti-submarine warfare; reduced radar, thermal and acoustic signatures. Size about 149 m, displacement about 6,670 tonnes; CODOG propulsion; max speed 28 knots (a knot is about 1.85 km per hour); BrahMos, medium-range air-defence missiles, hull-mounted sonar and helicopters.
• Sandhayak-class: hydrographic survey; multi-beam echo sounders, side-scan sonar and AUVs; about 110 m, 3,400 tonnes; speed over 18 knots; range 6,500 nautical miles; crew about 178; can operate helicopters and serve as a hospital ship. Indian hydrographers surveyed 89,000 square kilometres and produced 96 charts in five years (2019-24).
• Arnala-class: littoral anti-submarine warfare; about 77.6 m, 900 tonnes; waterjets; top speed about 25 knots; lightweight torpedoes and anti-submarine rockets; shallow-water sonar. INS Arnala is the largest waterjet-propelled warship yet inducted by the Navy. They replace ageing Abhay-class corvettes.

How do they fit India’s maritime vision?

• SAGAR (Security and Growth for All in the Region) was launched in 2015 for the Indian Ocean neighbourhood.
• MAHASAGAR (2025) widens that outreach across the Global South.
• Survey ships support the Blue Economy (about 4% of GDP). Defence exports were ₹23,622 crore in 2024-25, up about 12% from ₹21,083 crore in FY 2023-24.
• Project 17A engaged over 200 MSMEs and about 4,000 direct jobs, with over 10,000 indirect jobs.

How do the three classes compare?

Why does Nilgiri, Sandhayak and Arnala naval classes matter?

What are the challenges in Nilgiri, Sandhayak and Arnala naval classes?

• Serial production must keep pace with retirements of older ships.
• Littoral ASW needs training and sonar mastery, not only new hulls.
• Export success depends on after-sales support as much as build quality.
• Complex combat systems still need steady domestic electronics supply.

What should be done next on Nilgiri, Sandhayak and Arnala naval classes?

• Complete remaining Project 17A and Arnala / Mahe hulls on time.
• Use Sandhayak charts to deepen hydrographic cooperation with partners.
• Keep MSME vendor quality up as build rates rise.

What can Prelims ask on Nilgiri, Sandhayak and Arnala naval classes?

• Project 17A: 7 Nilgiri-class frigates; MDL and GRSE.
• Sandhayak-class: 4 survey vessels; INS Sanshodhak final.
• Arnala-class: 8 ASW SWC; Mahe-class at CSL takes planned total to 16.
• 21 Jun 2026: Dunagiri, Sanshodhak, Agray at Kolkata; 11 Jul 2026: Mahendragiri at Visakhapatnam.
• Indigenous content: 75% (P17A), over 80% (Sandhayak); 64 of 66 on-order hulls built in India.
• SAGAR 2015; MAHASAGAR 2025.

How to write about Nilgiri, Sandhayak and Arnala naval classes in Mains

Practice question (15 marks, 250 words): India’s naval modernisation rests on layered indigenous platforms. Discuss the roles of the Nilgiri, Sandhayak and Arnala classes.

• Intro: coast, EEZ, trade lanes; need for balance.
• Nilgiri: stealth surface combat, Project 17A.
• Sandhayak: hydrography and Blue Economy.
• Arnala: littoral ASW; Mahe-class expansion.
• Indigenisation, jobs, SAGAR/MAHASAGAR.
• Conclusion: from buyer’s navy to builder’s navy.