NEW DELHI — The Indian Navy will receive a major boost with the deployment of its second ballistic missile submarine. The INS Arighat is in the final stages of sea trials and is likely to be commissioned into service in early 2021.

INS Arighat is the second of the indigenous Arihant-class nuclear-powered ballistic missile-carrying submarine (SSBN).

Sources in the defence and security establishment said the submarine has performed well during the sea trials so far, and added that the commissioning of the vessel was delayed due to the coronavirus pandemic, according to Indian online newspaper.

Once Arighat enters service, India will be operating two SSBNs that are equipped with the 750km-range K-15 ballistic missile, designed for retaliatory strikes in case of a nuclear attack.

The Arighat was quietly launched in November 2017 by the then Defence Minister Nirmala Sitharaman.

Both INS Arihant, which is on operational deployment, and the Arighat have the capacity to carry four missiles each.

While the original plan was to have four Arihant class submarines, it was changed by the UPA government, sources in the know said.

Now, the two Arihant class submarines will have a displacement of 6,000 tons while two other SSBNs will be of a larger size (7,000 tons displacement).

A key differentiating factor will be that the two larger vessels under construction — S4 and S4 at the Ship Building Centre in Visakhapatnam — will have eight missile tubes instead of four.

India currently also operates a nuclear-powered attack submarine (SSN) INS Chakra II, which is under lease from Russia.

It was in March last year that India and Russia signed a $3 billion deal for the lease of a third SSN — Chakra III — that is likely to be in Indian waters by 2025 at the earliest.

Russian submarines are being leased to train crews for India’s own fleet of SSBNs.

In 2015, the Narendra Modi government gave the green light to build six indigenous SSNs. About two years later, in 2017, then Navy chief Adm. Sunil Lanba had confirmed that work on the SSNs had started.

It was in November 2018 that India completed its nuclear triad when PM Modi announced to the world the completion of the first deterrence patrol by Arihant.

With that, India joined an elite group of countries that have the capability to launch a nuclear weapon from land, air and underwater. The only other countries capable of this are the US, Russia, China and France.

INS Arihant was commissioned in 2016 by then Defence Minister Manohar Parrikar, but a formal announcement came only two years later.