Nilgiri-class frigate (2019)

Development . The frigates were designed by the Warship Design Bureau (formerly Directorate of Naval Design). 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. The P17A ships are geo-symmetrically larger by 4.54 % vis-à-vis P17, or the Shivalik-class frigates, and also features 75% indigenous content. On 28 November 2023, Bharat Heavy Electricals Limited (BHEL) received a contract worth to manufacture 16 Upgraded Super Rapid Gun Mounts (SRGMs) or Strales Systems for in-service ships as well as the under construction Nilgiri-class frigates. The state-owned firm Steel Authority of India Limited (SAIL) is supplying around 4,000 tonnes of steel for each of these ships. The steel is being manufactured in Bokaro, Bhilai, and Rourkela plants. 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 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-s, 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 – , , , , , and . 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. The ships are given names of mountain ranges in India. == 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. However, INS Udaygiri features the original, older Compact variant of the gun as noted during its commissioning. Originally, there were plans to install the Mk 45 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 . The ships are also equipped with two AK-630 each for close-in weapon system (CIWS) roles as well as multiple OFT-manufactured 12.7 mm M2 Stabilized Remote Controlled Gun. The launchers, designated Indigenous Rocket Launchers, have been manufactured indigenously by Larsen & Toubro. 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 360o, with the capability to track both aerial and surface targets, at a range of over . 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 , 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 is powered by 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 On 19 June 2009, the Defence Acquisition Council (DAC) — the main acquisition panel subordinate to India's Ministry of Defence (MoD) and chaired by the then Defence Minister of India A. K. Antony — cleared a proposal for the procurement of seven stealth frigates at a cost of under the designation Project 17A, as an advanced variant of s. The ships were to be constructed by Mazagon Dock Shipbuilders (MDL), Mumbai and Garden Reach Shipbuilders & Engineers (GRSE), Kolkata. The DAC also rejected the Navy's proposal of building two of the warships abroad. The construction of the warships will incorporate modular shipbuilding where 300-tonne prefabricated blocks would be put together similar to the construction style of . Earlier, on 4 December 2006, the Navy had sent out a pre-tender Request for Information (RFI) to French DCNS, Italian Fincantieri, American firms Lockheed Martin and Northrop Grumman besides shipyards in Russia and Korea for the construction of the first two ships by one of the foreign shipyards so as to ensure the timely absorption of the technology by the Indian shipyards. The project is expected to start in 2011 after both MDL and GRSE completes an upgrade to allow the modular construction. The deliveries were to begin 3–4 years after start of construction. All the firgates are to be inducted by 2022. As reported on 5 August 2013, the design of the Project 17A frigates along with Project 15B destroyers (now, s) were completed by the Directorate of Naval Design (DND) of the Indian Navy. Additionally, the cost negotiations for the construction of the seven vessels had been completed. As part of the project, MDL and GRSE will construct four and three frigates, respectively. Now, the Navy was awaiting clearance from the government. On 18 February 2015, the Cabinet Committee on Security (CCS) — India's top decision-making institution on matters related to defense and national security chaired by Prime Minister Narendra Modi — green-lighted the proposal for the Project 17A frigates at a cost of . The contract would be signed in the same month with an initial payment of . The project is the follow-on of the Shivalik-class or Project 17 frigates and the first ship by each the shipyards is expected to be delivered in 2022. Construction Garden Reach Shipbuilders & Engineers On 20 February 2015, the Indian Navy signed the contract with the Garden Reach Shipbuilders & Engineers (GRSE), a Kolkata-based public-sector shipyard, to build three frigates under Project 17 Alpha at an estimated cost of . According to the terms of the contract, GRSE is slated to deliver the three frigates in 2023, 2024 and 2025, respectively. The frigates would be constructed with "Integrated Construction Methodology" in partnership with Italy's Fincantieri. 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 . 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, , was launched on 14 December 2020, with its delivery slated to occur in August 2023. The second frigate, ', was launched on 15 June 2022, with its delivery expected in 2024. The final frigate, ', was launched in August 2023. 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". Himgiri was delivered to the Indian Navy on 31 July 2025 and was commissioned simultaneously with MDL's Udaygiri on 26 August 2025. The second ship from the GRSE lot, Dunagiri, was laid down on 24 January 2020, 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, Udaygiri, was launched on 17 May 2022, in a ceremony coinciding with the launch of , a . 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. and commissioned on 3 April 2026. The final ship from the MDL, Mahendragiri, was delivered to the Indian Navy on 30 April 2026. == Ships in the class ==

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. == Gallery ==

File:INS Nilgiri in Mumbai on September 28, 2019.jpg|The launch of INS Nilgiri, the lead vessel of the class. File:INS Nilgiri, INS Surat and INS Vagsheer during commissioning ceremony.jpg|INS Nilgiri during commissioning ceremony File:INS Udaygiri (F35) during sea trials.jpg|Udaygiri during sea trials File:INS Udaygiri, the second ship of Project 17A stealth frigate.jpg|INS Udaygiri during commissioning ceremony in July 2025 File:INS Taragiri top view.jpg|INS Taragiri top view ==See also==