The Project 75I-class submarine is a follow-on of the Project 75 Kalvari-class submarine for the Indian navy.
In the late 1990s, around the time of Kargil war, a three-decade plan took shape for indigenous construction of submarines.
It was known to have two separate series of submarine building lines – codenamed Project 75 and Project 75I — in collaboration with foreign entities.
Under this project, the Indian Navy intends to acquire six diesel-electric submarines, which will also feature advanced air-independent propulsion system.
This is for enabling them to stay submerged for longer duration and substantially increase their operational dates.

The submarines in the current Kalvari-class take their names from erstwhile decommissioned classes of submarines named kalavari.

It included Kalvari, Khanderi, Karanj and Vela class — which included Vela, Vagir, vagsheer.
Two submarines of the ongoing project, Kalvari and Khanderi, have been commissioned into the Indian
The third submarine, Karanj, is in the last phase of rigorous sea trails.
The fourth Scorpene, Vela, has commenced her sea trials, whilst the sixth and last submarine, Vagsheer, is being readied for boot together.

India currently operates one submarine each in nuclear-powered Classes of Chakra and Arihant and in addition to 14 submarines belonging to three classes of Diesel Electric category — Kalvari, Shishumar and Sindhughosh, some of which are ageing.

nuclear powered and diesel-electric submarines have their designated roles in the Carrier Battle Groups, which are formations of ships and submarines with Aircraft Carriers at the lead role.
As per the basic principles of submarine deployment and the minimum requirement for India to create a strategic deterrence, there is a specific number of submarines of both types that India needs to have in active service.
Currently, India has less number of submarines than what is required with some more of those from both types being at various stages of construction.

In maritime terms, a class of ships is a group of vessels which have the same make, purpose and displacement.
In the Navy and Coast Guard in India, the ships belonging to a particular class are named in a specific manner.
Many times the names have the same first letters, prefixes, similar meanings or the names belong to a particular type of words for example names of cities, persons, mythological concepts, animals, rivers, mountains, weapons, etc.
The class is generally named after the first vessel in the category. In some cases, a particular class of vessels takes their names from an earlier class of vessels which are now decommissioned.
Like Kalvari – which means Tiger Shark, Vagir has been named after a Sand Fish, a predatory marine
Khanderi has been named after an Island Fort built by Chhatrapati Shivaji, which played a key role in his Navy. Karanj has also been named after an Island located South of Mumbai.

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