'We may need four SSBNs and nine SSNs. Our current submarine fleet strength is 16.'

SSBN denotes submersible ship, with ballistic missile launch capacity and nuclear powered, whereas SSN implies submersible ship, nuclear powered.

The government has already approved the building of four SSBNs.

According to the officer, the commissioning of SSBN INS Arihant will take around two more years as all the systems have to be checked.

He said the nuclear submarine will be manned by a 100-member crew.

'The noise levels in the nuclear submarine are fine and the hull life is around 25 years.'

Queried about the reactor life, he added: 'Normally the hull and reactor life would coincide. The reactor will not be dismantled and fitted in another submarine.'