Soviet Union-built submarine was commissioned on January 4, 1990. The cost of the retrofitting project at HSL is estimated at around Rs.700 crore.

The sea trial of Russia-made INS Sindhukirti, the seventh Sindhughosh class diesel electric submarine of Indian Navy, was launched after successful completion of retrofitting at Hindustan Shipyard Limited here on Thursday.

“Today is a red-letter day in our history as retrofitting involved a complex process -- a more difficult process than building a new submarine. Our workforce deserved credit for completing the Herculean task adhering to stringent quality standards stipulated by the Navy,” Rear Admiral N.K. Mishra told The Hindu.

The HSL, the premier shipyard of the country set up in 1941 had earlier completed retrofitting of two submarines belonging to Egyptian naval forces and INS Vagli.

“This was the biggest-ever repair of a submarine undertaken in any shipyard in the country proving our capability to take up orders to construct generation next Greenfield submarines,” Mr. Mishra said.

The INS Sindhukirti was built at Admirality Shipyard and Sevmash in the erstwhile Soviet Union and commissioned on January 4, 1990. The cost of the retrofitting project is estimated at around Rs.700 crore to Rs.800 crore.

The delayed completion of the submarine is attributed to insistence by the Russians to source electrodes and several parts from their country including change of mainline cables in 2011, according to sources.

The HSL also had to undertake dredging after undocking it on November 4 due to accumulation of sand in its area reducing the draft from seven to four metres under the influence of Cyclone Hudhud, which battered the industries of Visakhapatnam on October 12, 2014.