Vishakapatnam, July 26 - India Sunday joined a select group of five nations with the launching here of the country's first indigenously designed and built nuclear-powered attack submarine, which Prime Minister Manmohan Singh described as a 'historic milestone' in the country's defence preparedness.

The prime minister's wife Gursharan Kaur did the honours of launching the submarine - INS Arihant - at a function here.

Manmohan Singh, speaking at the event, assured that the nuclear submarine was not developed with 'aggressive designs' or to 'threaten anyone', but it was necessary to take all measures to safeguard the country and keep pace with technological advancements in the world.

He also congratulated the Advanced Technology Vehicle (ATV) Programme and the people associated with it for designing and building the nuclear submarine, which he said was a reflection of the 'immense technical expertise' and the strength of the research and development organisations in the country.

'Today we join a select group of five nations who possess the capability to build a nuclear powered submarine,' the prime minister said. The other countries are the US, Russia, China, France and Britain.

'The construction of a submarine is a highly demanding task by itself. For the country to develop its first nuclear submarine is a special achievement.

'I congratulate the Advanced Technology Vehicle (ATV) Programme and all personnel associated with it for achieving a historic milestone in the country's defence preparedness. Today's launch is a reflection of the immense technical expertise that exists in our country and the strength of our research and development organisations,' the prime minister said.