[16] Ultimately, the IN chose the latter, reasoning that the Scorpène, which had been offered with a provision of technology transfer (TOT), was more advanced than the Type 209/1500.

[16] It was also thought that the Scorpène design won the deal because of its capability to fire Exocet anti-ship missiles and an agreement on the air-independent propulsion (AIP).

[17] Batch-I:On 6 October 2005, India signed a series of contracts for transfer of technology to construct six submarines at MDL with Armaris, along with the supply of SM39 Exocet missiles manufactured by MBDA.

Valued at a then-total cost of €2.4 billion,[18] the deal included a 30% offset clause and a delivery timeline wherein the six ordered units were to be delivered between 2012 and 2017.

[21] In December 2023, MDL submitted a bid to construct the three submarines, equipped with higher measures of indigenously-developed technology along with an AIP module for enhanced underwater endurance.

[23] The entire upgraded combat management system for the Batch II submarines will be indigenously developed by Bharat Electronics Limited.

[3][28] However, work stalled when public disclosures revealed that the 2005 agreement had omitted the procurement of specific components, including engines, generator and raw materials.

[30] Protracted negotiations between the MoD and DCNS for the components lead to the additional sanctioning of ₹4,764 crore by the CCS, which further delayed the project by two years.

[47][48] On 22 June, Larsen & Toubro signed a contract with DRDO for the construction of two units of AIP system modules for the Kalvari class.

The facility was constructed by Larsen & Toubro and is equipped with a five-metre (16 ft) escape tower integrated with an adjacent diving basin.

[52][53][54] On 30 December, the Indian Ministry of Defence signed two contracts with Mazagon Dock Limited (MDL) and Naval Group, France for upgrades related to the Kalvari-class submarines.

The first contract, the one signed with MDL [worth ₹1,990 crore (US$230 million)], is for the construction and integration of AIP Plug into Batch 1 submarines,[55] while the second contract signed with Naval Group [worth ₹877 crore (US$100 million)] is for the integration of indigenous Electronic Heavy Weight Torpedo (EHWT) systems.

[61] The submarine is powered by two 1,250 kW MAN diesel engines, which are complemented 360 battery cells (750 kg, 1,650 lb each) that powers a Permanently Magnetised Propulsion Motor for extremely-silent underwater operation, thus allowing it have an operational range of around 6,500 nautical miles (12,000 km; 7,500 mi) at 8 knots (15 km/h; 9.2 mph) when surfaced.

[4][62][63] The six Batch-I submarines are expected to retro-fitted with an indigenously developed AIP modules during their respective mid-life refits, starting with Kalvari in September 2025.

The three Batch-II submarines, in turn, will be equipped with the AIP modules during the construction with technological oversight from Naval Group.

On 22 June 2023, L&T and DRDO signed a contract to manufacture two units of Air Independent Propulsion (AIP) System Modules.

The manufacturing, integration and factory acceptance trials of the Energy Modules (EMs) will be conducted at L&T’s AM Naik Heavy Engineering Complex at Surat.

[58][72] On 30 December 2024, Mazagon Dock received a contract, worth ₹1,990 crore (US$230 million), for the fabrication of AIP Plug and its integration into the submarines.

[79] On 24 March 2024, a Kalvari-class submarine reached Campbell Bay, the southernmost port of India in the Nicobar Islands, for the first time.

[82][83][84] In an incident on 22 November 2024, a submarine of the Kalvari class collided with a fishing boat about 70 nautical miles (130 km; 81 mi) off the coast of Goa.