With the commissioning of the INS Arihant in 2016, India joined a select group of countries— the US, Russia, China, France, and the UK—which builds and operates Ship Submersible Ballistic Nuclear (SSBN) submarines. The second SSBN under the project is likely to be commissioned very soon.

India has launched its third Arihant-class ballistic missile submarine (SSBN), the S-4, satellite imagery confirmed on Wednesday. The unnamed submarine is much longer than the first two vessels of the class.

The Arihant class SSBNs are critical to the nuclear triad of land, sea, and air-launched weapons.

H I Shutton, one of the world's leading experts on underwater warfare and submarine technology, has analysed the high-resolution satellite images and claimed that the S-4 is about 20 metres longer than its predecessors, at 110 metres in length.

With an improved reactor, the new submarine has eight missile tubes instead of four in the earlier two boats.

"The hull diameter does not appear to have increased and the missile deck remains narrow", Shutton said.

The submarine is equipped with K-4 and K-15 submarine-launched ballistic missiles. The K-4 nuclear-tipped ballistic missile can hit a target at a range up to 3,500 km, while the 10.8-metre K-15 Sagarika has a range of 1,500 km.

The submarine will also be armed with Russia's Type 53-65 wake-homing anti-ship and Test-71 autonomous and remotely controlled torpedoes.

India currently has one SSBN, the INS Arihant, in service, while the commissioning of the second vessel of this class has been delayed due to the pandemic.

The Indian Navy has been expanding its submarine fleet amid the growing capabilities of the naval forces of neighbouring Bangladesh, Myanmar, and Pakistan.

Myanmar inducted a diesel-electric submarine of Chinese origin on 24 December, while Bangladesh received two Ming-class submarines in 2017 under a multi-million defence deal with China. Pakistan will induct eight Type-039A Yuan-class submarines by 2027.