# Nilgiri-class frigate (2019)

The Nilgiri-class frigates, formally classified as the Project-17 Alpha frigates (P-17A), are a series of stealth guided-missile frigates currently being built by Mazagon Dock Shipbuilders (MDL) and Garden Reach Shipbuilders & Engineers (GRSE) for the Indian Navy (IN).
Designed by the Warship Design Bureau, the class is intended to serve as a complement to the currently-serving Shivalik-class frigates (P-17) with improved design portfolios, such as low radar cross-section (RCS) and reduced infrared signature.
With a total of seven vessels, the construction of the frigates are currently divided between MDL and GRSE. As of 2024, all seven frigates have been launched and are intended to enter service with the IN between 2024 and 2027. The frigates will form a part of the Eastern Fleet as well as the future Carrier Battle Group (CBG) of INS Vikrant.
Upon entering service, the class is to be complemented by an additional series of seven or eight frigates, under the codename the Project-17B series.

## Design
### Development

The frigates were designed by the Warship Design Bureau (formerly Directorate of Naval Design) – an internal establishment within the Indian Navy responsible for designing warships; the organisation is also distinguished for having contributed to the designing of numerous Indian warships, including INS Vikrant – India's first indigenously-designed aircraft carrier, the Arihant-class submarines – India's first indigenously-designed nuclear-powered ballistic missile submarines and the Shivalik-class frigates – India's first indigenously designed frigates equipped with stealth technology.
The class' design was finalised by the DND in 2013; it was later unveiled to the public in April 2018, when MDL displayed a scale model of the frigate at the DefExpo 2018 military exhibition, held at Chennai, India.
On 5 September 2018, Mazagon Dock Shipbuilders (MDL) and Garden Reach Shipbuilders & Engineers (GRSE) awarded Bharat Electronics (BEL) with a ₹9,200 crore (equivalent to ₹120 billion or US$1.4 billion in 2023) contract to supply seven Barak 8 LR-SAM air defence systems for Nilgiri-class frigates. In October 2018, Bharat Electronics signed a $777 million deal with Israel Aerospace Industries to help fulfil the Barak-8 order.
On 28 November 2023, Bharat Heavy Electricals Limited (BHEL) received a contract worth ₹2,956.89 crore (US$340 million) to manufacture 16 upgraded Super Rapid Gun Mounts (SRGMs) for in-service ships as well as the under construction Nilgiri-class frigates.

### Features
#### Stealth

The frigate's design incorporates a significant degree of stealth and low radar-observability – through the utility of composite materials, radar-absorbent coatings and low-observable/radar-transparent technologies; the usage of the aforementioned materials assists the vessel in maintaining a low radar cross-section (RCS).
The vessel's physical profile also features a substantial level of stealth through the application of different physical forms – including an enclosed mooring deck, flush deck-mounted weapon systems and a reduced number of antennae.
The frigate's infrared signature, most specifically emissions from its propulsion exhaust and power generation machinery, are reduced through the application of Venturi effect and fluid injection, which helps to reduce the plume and hot metal temperatures of exhaust. To maintain acoustic silence, the frigate is equipped with propellers designed to have onset of cavitation at higher speeds to reduce hydrodynamic noise. In addition to the propellers, the vessel's hull also features special acoustic enclosures for some of the machinery to reduce the emission air-borne noise.

#### Modular profile

The P-17A frigates are the first major class of Indian-designed warships to be built using the methodology of integrated modular construction – a manufacturing process in which multiple modules (or "blocks") of a vessel's hull are pre-assembled/pre-outfitted independently, before being aggregated for final assembly.
In December 2015, MDL contracted Fincantieri S.p.A. to provide technical assistance and essential expertise in the construction of the seven frigates using the "modular construction" methodology.

### Naming

The P-17A frigates were named after the former-Nilgiri-class frigates, which served in the IN between 1972 and 2013; the first six ships of the series were allotted the names utilised by the older class, namely – Nilgiri, Himgiri, Taragiri, Udaygiri, Dunagiri, and Vindhyagiri. The seventh and final vessel of the P-17A series, which did not have a namesake from the older class, was given the new name of Mahendragiri.

## Instrumentation
### Armament
#### Anti-surface warfare

As part of its anti-surface warfare (ASuW) capabilities, the class features eight VLS-launched BrahMos anti-ship cruise missiles, capable of speeds of up to Mach 3. The BrahMos is widely regarded as one of the most formidable anti-ship missiles currently in service, given the missile's extreme versatility and manoeuvrability.
The vessels are equipped with one upgraded OTO Melara 76 mm naval gun for anti-missile/anti-aircraft roles. The upgraded guns manufactured by Bharat Heavy Electricals Limited (BHEL) features the Strales system with DART ammunition firing capability.
Originally, there were plans to install the Mk 45 127 mm (5 in) naval gun, manufactured by BAE; however, this plan was later scrapped in 2021 on account of financial constraints.

#### Anti-air warfare

As part of its anti-air warfare (AAW) capabilities, the class features thirty-two Barak 8 surface-to-air missiles, with eight missiles present in four 2×4 VLS configurations – with two placed at the bow and two placed aft.
The LR-SAM is an extended-range variant of the original Barak 8 and is designed to neutralize various aerial threats, including fighter aircraft, helicopters, anti-ship missiles, cruise missiles, ballistic missiles and unmanned aerial vehicles (UAV). This variant has a range of about 100 km (62 mi).

#### Anti-submarine warfare

As part of its anti-submarine warfare (ASW) capabilities, the class features two triple-tube lightweight torpedo launchers for firing Varunastra ASW torpedoes. The class also features two RBU-6000 (RPK-8) anti-submarine rocket launchers, capable of firing ASW projectiles to depths of up to 1,000 m (3,280 ft 10 in).

#### Decoys

During the class' unveiling in 2018, the frigate's design was noted to possess two anti-torpedo decoy systems and four decoy launchers – which presumably may be the NSTL Maareech torpedo-countermeasure system and the Kavach anti-missile decoy launchers, respectively.

#### Aviation facilities

As part of its aviation facilities, the class is equipped with a flight-deck and an enclosed aviation hangar, capable of accommodating a single naval helicopter – most likely the ALH Dhruv MK-III maritime-reconnaissance helicopters, or the Westland Sea King Mk. 42B ASW/ASuW helicopters – both of which are operated by the Indian Naval Air Arm.

### Sensors
#### Radar

The class features the EL/M-2248 MF-STAR active electronically scanned array (AESA) radar as its primary radar suite. The EL/M-2248 is a multi-function, phased-array radar system featuring an azimuth of 360$^o$, with the capability to track both aerial and surface targets, at a range of over 450 km (280 mi).
The class also features the Indra LTR-25 'Lanza' surface-search radar, as its secondary radar suite. The LTR-25 is a solid-state, three-dimensional (3D), long-range radar capable of operating in a dense electronic environment and features a range of over 250 nmi (460 km; 290 mi), with the capability to track various aerial targets – including fighter aircraft and ballistic missiles.
The frigates are also equipped with an advanced combat management system, classified as "CMS-17A", which is reportedly equipped with sophisticated data links for high, efficient interoperability with other naval vessels.

#### Sonar

The class is equipped with the BEL HUMSA-NG sonar, developed by the DRDO. The HUMSA-NG is a hull mounted "active cum passive" integrated sonar system capable of detecting, localizing, classifying and tracking sub-surface targets in both active and passive modes.

#### Electronic warfare

The frigates feature the Shakti electronic warfare (EW) suite – developed by the Defence Electronics Research Laboratory (DLRL), for defense against anti-ship missiles and for the interception, detection, classification, identification and jamming of conventional radars. Shakti is equipped with wide-band electronic-support measures (ESM), electronic countermeasures (ECM), an integrated "Radar Finger Printing System (RFPS)" and a data-recording replay feature for "post-mission analysis".

### Propulsion

Each frigate features two General Electric LM2500 gas turbines – manufactured by GE Aviation and two MAN 12V28/33D STC four-stroke engines – manufactured by MAN Diesel & Turbo, arranged in a combined diesel and gas (CODAG) propulsion configuration.
In December 2016, the IN contracted GE Aviation to supply fourteen LM2500 gas turbines for the seven frigates, which were license-assembled in India by the Industrial & Marine Gas Turbine Division (IMGT) of Hindustan Aeronautics Limited (HAL). Under the deal, HAL was additionally sanctioned to provide comprehensive services – including the supply of spare parts, maintenance inspections and equipment overhauls.
At the time of the order, HAL had already delivered eleven LM2500 turbines to the IN; the turbines are specifically used on multiple Indian warships, most notably on the Shivalik-class frigates.
In February 2019, MDL contracted GE to supply an assortment of auxiliary equipment to the IN to support the fourteen engines; under the agreement, GE also handled the design work of the frigate's auxiliary system and its fuel supply system.
In May 2016, the IN contracted MAN Diesel & Turbo to supply fourteen MAN 12V28/33D STC four-stroke engines for the seven frigates; under the deal, the requisite parts needed for the engines were sourced from India, while the engines' final assembly and testing were conducted at MAN's facility in Aurangabad, India.

## History
### Background

In June 2009, the Defence Acquisition Council (DAC) – the main acquisition panel subordinate to India's Ministry of Defence (MoD), cleared a proposal for the procurement of seven stealth frigates at a cost of ₹45,000 crore (equivalent to ₹1.1 trillion or US$13 billion in 2023) crore – classified as "Project 17A" – on the lines of the IN's initiative of establishing a 160-ship fleet.
In September 2012, the Cabinet Committee on Security (CCS) – India's top decision-making institution on matters related to defense and national security, green-lighted the proposal for the "development cum construction" of the seven frigates. Initially, the IN favoured a proposal of building the first two frigates at a foreign shipyard – seeking to minimize the project's overall construction timeline; however, this suggestion was overruled by India's Ministry of Defence (MoD) – which favoured indigenous production of the frigates.
The seven frigates were envisioned as a "follow-on series" to the Shivalik-class frigates (Project 17), which were also being built for the IN at the time, but equipped with more sophisticated capabilities. The designing-process of the seven frigates was completed in mid-2013. The project – consisting of the construction of the seven designated frigates over a span of five years – was formally approved by the CCS in February 2015.

### Construction

The seven frigates are to be jointly constructed by two public-sector shipyards, namely, MDL and GRSE, with four of the frigates allotted to MDL and the remaining three allotted to GRSE.

#### Garden Reach Shipbuilders & Engineers

In February 2015, the IN contracted Garden Reach Shipbuilders & Engineers (GRSE), a Kolkata-based public-sector shipyard, to build three P-17A frigates at an estimated cost of ₹19,294 crore. According to the terms of the contract, GRSE is slated to deliver the three frigates in 2023, 2024 and 2025, respectively. In preparation for the order, GRSE re-augmented its infrastructure by establishing newer, modular shipyards along with a Goliath gantry crane, meant for enabling the construction of the frigates in a short time frame.
A significant proportion of the hull's blocks needed for the vessel's construction was procured from smaller shipyards and metal fabrication shops in and around Kolkata, while the construction/fabrication of additional infrastructure was done at GRSE's Rajabagan shipyard.
Construction reached a hiatus in April 2018, when the shipyard's Goliath crane, having failed to withstand strong cyclonic winds which had been travelling at around 100 km/h (62 mph). The accident rendered the crane permanently inoperable, whilst the module hall - which was to have fabricated the modular blocks for the future frigates, was rendered unusable. However, no damage was reported to have been inflicted on the vessels that were being built by the shipyard, according to representatives from the IN and GRSE.
The mishap forced GRSE to modify the project's timeline, by prioritizing the construction of the modular blocks at its other facilities, rather resuming constructing post-repairs to the shipyard. With the loss of the crane, GRSE resorted to building smaller 50 t and 100 t blocks (instead of the regular 250 t blocks) with the shipyard’s smaller cranes. In 2021, GRSE installed a Goliath crane that had purchased from South Korea, with a lifting capacity of 250 t, thus resuming regular construction operations.
The construction of the first frigate began in November 2018, while work on the second and third frigates began in January 2020 and March 2021, respectively. The first of the three frigates, Himgiri, was launched on 14 December 2020, with its delivery slated to occur in August 2023. The second frigate, Dunagiri, was launched on 15 June 2022, with its delivery slated to occur in 2024.
On 3 March 2025, GRSE completed the Contractor Sea Trials (CST) of INS Himgiri was completed by GRSE along with INS Androth. As per a press release, "CST is considered the final stage of construction, when a vessel’s seaworthiness is tested".

#### Mazagon Dock Shipbuilders Limited

In February 2015, the IN contracted Mazagon Dock Shipbuilders Limited (MDL), a Mumbai-based public-sector shipyard, to build four P-17A frigates at an estimated cost of over ₹21,000 crore. According to the terms of the contract, MDL is to deliver the four frigates in 2022, 2023, 2024 and 2025, respectively.
The four frigates were built at different locations, namely, at MDL's main shipbuilding facility in Mumbai, at MDL's subordinate facility in Nhava, at a smaller shipbuilding facility also operated by MDL in Mumbai, at an MSE shipyard in Gujarat and at another shipyard in Goa. Similarly to GRSE, MDL also upgraded its existing infrastructure; the shipyard augmenting its existing facilities with newer equipment, including a "Goliath" gantry crane, a module workshop, a wet basin and a "cradle assembly" shop, meant to facilitate modular construction.
The construction of the first frigate began in December 2017, while work on the second, third and fourth frigates began in May 2019, September 2020 and June 2022, respectively. The first of the four frigates, Nilgiri, was launched on 28 September 2019, and began its sea trials five years later, in August 2024.
The second frigate of the four frigates, Udaygiri, was launched on 17 May 2022, in a ceremony coinciding with the launch of INS Surat, a Visakhapatnam-class destroyer. The third frigate, Taragiri, was launched on 11 September 2022, and is scheduled to be delivered by 2025.
Nilgiri was commissioned into the Indian Navy service on 15 January 2025.

## Ships in the class

| Name | Pennant | Yard Number | Builder | Laid Down | Launched | Commissioning | Status |
| Indian Navy ||||||||
| Nilgiri | F33 | 12651 | Mazagon Dock Shipbuilders Limited (MDL) | 28 December 2017 | 28 September 2019 | 15 January 2025 | Active |
| Udaygiri | | 12652 | Mazagon Dock Shipbuilders Limited (MDL) | 7 May 2019 | 17 May 2022 | March 2025 (expected) | Launched |
| Taragiri | | 12653 | Mazagon Dock Shipbuilders Limited (MDL) | 10 September 2020 | 11 September 2022 | 2026 (expected) | Launched |
| Mahendragiri | | 12654 | Mazagon Dock Shipbuilders Limited (MDL) | 28 June 2022 | 1 September 2023 | 2027 (expected) | Launched |
| Himgiri | | 3022 | Garden Reach Shipbuilders & Engineers (GRSE) | 10 November 2018 | 14 December 2020 | August 2025 (expected) | Contractor sea trials completed |
| Dunagiri | | 3023 | Garden Reach Shipbuilders & Engineers (GRSE) | 24 January 2020 | 15 July 2022 | Q1 2026 (expected) | Launched |
| Vindhyagiri | | 3024 | Garden Reach Shipbuilders & Engineers (GRSE) | 5 March 2021 | 17 August 2023 | Q3 2026 (expected) | Launched |

## Export

In August 2024, the Mazagon Dock Shipbuilders offered to the Brazilian Navy, the project for a joint construction of up to six Project-17 Alpha frigates, to attend the requirement of Brazil for a new class of 6,000 tons vessels, to operate in conjunction with the newest Tamandaré-class frigates.