The first Project 971 is already being upgraded at the Zvezdochka shipyard. The overhaul of the submarine must be complete in 2 years before it will rejoin the Russian Navy. The upgraded submarines will have a reduced signature to make them harder to detect and improved electronics.
The Project 971 submarines were developed by the Malakhit Design Bureau as a cheaper alternative to the more expensive titanium-hulled Project 945 / Sierra class submarines, which are also to be upgraded and returned to service.
These submarines will be joined by new Project 885 Yasen or Graney class submarines that are now under construction to form the backbone of Russia's nuclear attack submarine fleet.
A total of 15 Project 971 submarines have been build and are subdivided into 4 different subclasses:
- the project 971 or Akula-I class
- the Project 971I or Akula-I class
- the Project 971U or Akula-II class
- the Project 971M
- their length varies between 110 to 113 m
- their submerged displacement varies from 12700 tons to 13800 tons
- later units have a reduced complement
- later units can dive deeper
- the sail has been enlarged on later units
Some of the 15 Project 971 submarines are out of service and may not be bought back. One of the them, the Nerpa, has been leased to India for 10 years, starting in 2012, and where it is known as the INS Chakra.
The INS Chakra is known to be different from its counterparts in the Russian Navy. Among others, it lacks many of the sensors that are present on the Russian units. Equipment installed may not be identical to Russian ones.
The 650 mm torpedo tubes have also been removed and it is not compatible with the more advanced weapons available. The INS Chakra is therefore not as capable a submarine as those in Russian service.
Before handover to the Indian Navy, the Nerpa suffered an accident in 2008 that killed 20 people. This accident was said to have been caused by gas released by the fire extinguishing system.