The plan for the Advanced Technology Vessel (ATV) until the late 1980s was to build an SSN – a fast-moving deep-diving nuclear-powered attack submarine, which would hunt surface ships.  

• Around the time India leased a Charlie-I class nuclear-powered attack submarine from the Soviet Union, which happened in 1988, planning veered towards building a submarine carrying ballistic missiles.  
• The hull design was lengthened and the SSN quietly transformed into an SSBN. The Project code named Advanced Technology Vessel (ATV) Project took 25 years for completion.  

• It spawned a new era in the field of cooperation between DRDO, BARC, Navy, PSUs and private industry in which these organizations synergized their efforts to achieve a significant technological and strategic milestone.  
• The Arihant class (nuclear-powered ballistic missile submarines)- INS Arihant (S73), INS Aridhaman (S74) are built for the Indian Navy by Navy Shipbuilding Centre, Visakhapatnam.  
• The miniaturised naval version of the reactor was designed and built by the Bhabha Atomic Research Centre (BARC) at the Indira Gandhi Centre for Atomic Research (IGCAR) in Kalpakkam. 

Source: The Hindu