This is coolbert:
From MARCO POLO through Harry:
"India's Hindustan Shipyard Limited recently announced that one of the Indian Navy's diesel-electric submarines -- 'Sindhukirti' -- had completed a large-scale modernization work, and was now under sea trials. The work on the submarine had started in 2006. Therefore, it took nine years to be completed! The work was performed at the company's yard in Vishakhapatnam (south-eastern India), in which Russian engineers participated. On that submarine, 100-kilometer long electrical wires and 30-kilometer long compression piping were replaced. A new sonar system, called 'Ushus' was installed. Besides, hundreds of other new systems, both Indian and foreign, were installed. The shipyard says that it is far more difficult to modernize a submarine than to build one from the scratch."
. . . .
"These submarines are all Russian-built 'Project 887EKM (NATO's 'Kilo')' type."
It can be reasonably suggested that by the time the submarine has completed the modernization process to an extent is already out-of-date?
The modern nuclear powered submarine of the HMS Astute class the most complicated thing made by man. I might think also a diesel/electric Kilo class boat even if not brand-new not so very far behind in complexity.