The ?70,000-crore Project 75(I) program provides for six conventional attack submarines featuring 21-day continuous submerged endurance via German polymer-electrolyte-membrane hydrogen fuel cells. Under contractual terms, Mazagon Dock Shipbuilders Limited and ThyssenKrupp Marine Systems will deliver the first vessel within seven years of signing, escalating indigenous manufacturing content from 45% on the lead hull to 60% by the final delivery.

According to NDTV on August 16, 2026, India is approaching the final Cabinet Committee on Security decision on Project 75(I), a programme to build six diesel-electric attack submarines at Mazagon Dock Shipbuilders Limited in Mumbai with ThyssenKrupp Marine Systems, at a current headline value of roughly ?70,000 crore ($7.310 billion), after a procurement process that has extended across more than 25 years. The Finance Ministry cleared the acquisition on May 28, 2026, leaving CCS authorization as the remaining major government approval, with the proposal expected to reach the committee in August and contract conclusion targeted by September 2026.

The delay is more significant: Project 75(I) derives from the 30-year submarine construction plan approved on July 12, 1999, under which India intended to produce 24 conventional submarines through two parallel foreign-assisted lines of six boats each, then build another 12 incorporating indigenous design expertise accumulated from the first two series. That timetable envisaged the first 12 submarines being produced within roughly 12 years, but by August 2026 only the six Project 75 Kalvari-class boats had emerged. P-75(I) itself passed through approvals in 2010, 2014, and January 2019 before reaching its present acquisition phase. Even a contract signed in 2026 does not provide a near-term fleet solution: the first submarine is contractually required seven years after signature, and operational induction has also been projected for 2034-35, when most of the Navy’s current submarines will be more than 40 years old.

The P-75(I) competition was progressively reduced from seven foreign designs to a single compliant MDL-TKMS team, principally because India required an AIP installation already demonstrated aboard an operational submarine rather than a system still awaiting sea service. The designs considered at different stages included TKMS’s Type 214 from Germany, Naval Group’s Scorpène and diesel-electric Barracuda-derived concepts from France, Rubin’s Amur-1650 from Russia, Saab’s A26 Blekinge-class from Sweden, Mitsubishi Heavy Industries’ Soryu-class from Japan, Navantia’s S-80 Plus from Spain and DSME’s KSS-III derivative from South Korea. By January 2020, five foreign suppliers remained: TKMS, Naval Group, Navantia, DSME and Rubin, while MDL and Larsen & Toubro were the two Indian shipyards authorized to form competing industrial teams.

The July 2021 RFP changed the competitive balance by requiring an operational, sea-proven AIP system. Saab had already withdrawn; Russia subsequently withdrew because it could not satisfy the requirement set; Naval Group left the competition in April 2022 because its proposed submarine could not provide the required fuel-cell AIP installation; and DSME later ceased participating, reducing the contest to MDL-TKMS and L&T-Navantia. Both remaining proposals passed the Indian Navy’s initial technical evaluation in February 2024. Indian teams then evaluated the German solution at Kiel in March 2024 and the S-80 Plus at Cartagena in June 2024, but Navantia’s AIP installation did not meet the requirement for an operational system already proven at sea.

L&T-Navantia was formally eliminated in January 2025, making MDL-TKMS the sole compliant bidder and allowing MDL’s commercial proposal to move into cost negotiations. Procurement agencies began negotiations with MDL on September 10, 2025; the Cost Negotiation Committee completed the process by January 16, 2026; the Finance Ministry cleared the acquisition on May 28; and the remaining technology-transfer assessment was expected to precede CCS referral in August. The P-75(I) submarine emerging from this process will be substantially different from a standard Type 214. Existing Type 214s generally occupy the 1,700-2,000-tonne surfaced displacement category, while the Indian design will possess a displacement near 3,000 tonnes and a longer hull adapted to Indian endurance, weapons, sensor and acoustic signature requirements.

This means the dimensions of the Greek Papanikolis, Portuguese Tridente, South Korean Son Won-il or Turkish Reis derivatives cannot simply be transferred to P-75(I), because the Indian submarine is being redesigned rather than reproduced unchanged. The underlying propulsion architecture remains diesel-electric with a single shaft, batteries, and Siemens polymer-electrolyte-membrane hydrogen fuel cells for AIP operation. Existing Type 214 subclasses include a submerged speed of 20 knots, a surfaced range of 12,000 nautical miles, a submerged battery range of 420 nautical miles at 8 knots or 1,248 nautical miles at 4 knots, endurance of 84 days, a diving depth close to 400 metres, and eight 533 mm torpedo tubes, four of which can support Sub-Harpoon missiles in applicable configurations.

The Indian configuration is expected to retain 533 mm tubes while incorporating a considerably heavier weapons requirement, including 18 heavyweight torpedoes and at least 12 cruise missiles for anti-ship and land-attack missions. Compared with India’s Kalvari-class, which displaces 1,615 tonnes surfaced and 1,775 tonnes submerged, measures 67.5 metres long and 6.2 metres wide, reaches 20 knots submerged and has a 350-metre test depth, the P-75(I) is therefore a significantly larger SSK for longer Indian Ocean patrols. A conventional diesel-electric submarine uses battery power while completely submerged, but once battery state falls below the level required for continued operations, its diesel generators need atmospheric oxygen to restore charge. That normally requires the submarine to approach the surface and raise a snorkel.

The operating cycle in the P-75(I) places conventional diesel-electric submarines at a snorkelling interval of roughly every 48-72 hours, while the German PEM fuel-cell AIP system can keep the submarine submerged for 21 consecutive days under low-speed conditions. In practical terms, a P-75(I) using AIP at patrol speed could avoid seven to ten recurring periods in which a non-AIP submarine would otherwise need to move close to the surface, expose its snorkel and operate diesel machinery. Fuel cells generate electrical power efficiently and quietly but at much lower output than the power demanded for sustained high-speed submerged movement, so the submarine still depends on batteries for high-power manoeuvres. The advantage is therefore endurance at patrol speed and reduced exposure, particularly when holding a choke point, conducting surveillance or waiting in an assigned sea-denial area.

The difference is especially significant because the Indian Navy’s current conventional fleet combines six relatively new Kalvaris with ten submarines commissioned between 1986 and 2000. INS Sindhughosh was decommissioned on December 19, 2025, after 40 years of service, reducing the SSK inventory to 16 boats. The modern component consists of INS Kalvari commissioned in 2017, INS Khanderi in 2019, INS Karanj and INS Vela in 2021, INS Vagir in 2023, and INS Vagsheer in 2025. Those six boats account for 37.5% of the conventional fleet. The remaining 62.5% consists of six older Sindhughosh-class Kilos and four aging Shishumar-class Type 209/1500s. The surviving Kilos are INS Sindhuraj from 1987, INS Sindhuratna and INS Sindhukesari from 1988, INS Sindhukirti from 1989, INS Sindhuvijay from 1991 and INS Sindhurashtra from 2000.

The Shishumar force consists of INS Shishumar and INS