Prime Minister Manmohan Singh called the event a "giant stride in ... our indigenous technological capabilities."
It's the first nuclear-powered submarine built in India and the first such vessel constructed by a country other than the United States, U.K., France, Russia or China.
Reports of the vessel suggest its design is based on Russia's Akula-class submarines, which came into operation toward the end of the Cold War. India has leased one from Moscow and plans to operate others. However, unlike the Akula, which is an attack submarine, Arihant is designed to be the first in a class of Indian boats that carry ballistic missiles.
The BBC says:
"Nuclear [ballistic missile] submarines will add a third dimension to India's defence capability, as it has previously only been able to launch ballistic missiles from the air and from land. ...Naval-technology.com adds:
"The fact that this submarine, the nuclear reactor that powers it, and the ballistic missiles that it will fire are all manufactured locally in India — though there may have been some assistance from Russia — is a significant technological achievement."
"The Indian Navy has a fleet of 16 diesel-electric submarines leased from Russia and Germany. However, the disadvantage with diesel electric submarines is that they cannot stay under water for an extended period.The website says the cost of building the Arihant is estimated at $2.9 billion.
"Conventional diesel-electric submarines have to ascend to the surface each day to eject carbon dioxide produced by the generator. Nuclear-powered submarines, on the other hand, can stay under water for long durations without being detected."