The Indian Navy's P-16A Brahmaputra-class guided missile frigate INS Betwa has been set upright on even keel at the Naval Dockyard in Mumbai.

The frigate keeled onto its side during undocking on 5 December last year while undergoing major upgrade operations, killing two sailors and injuring another 14.

US-based salvage firm Resolve Marine Group was awarded a Rs20cr ($2.9m) contract in January to lift the 3,850t INS Betwa.

Initial stabilisation of the vessel was achieved by 29 December last year, and the complete salvage operation was concluded in less than two months. The works included complex hydrodynamic calculations and rigging up of intricate measuring and monitoring systems.

The quick salvage operation was made possible as the majority of the machinery used on the vessel had already been removed from the ship during renovation, which had been ongoing since April last year.

"Initial stabilisation of the vessel was achieved by 29 December last year, and the complete salvage operation was concluded in less than two months."

Equipment was removed either for routine servicing or for replacement with newer, more advanced systems.

According to the Indian Navy, INS Betwa will become completely operational by its scheduled date of refit completion in April last year, thanks to in-house expertise and continued repair efforts.

The Times of India reported the Brahmaputra-class frigate first slipped from its dock blocks and then tilted before falling on its side, citing unnamed sources from the Naval Board of Inquiry (BoI).

Sources state that the incident occurred as a result of a miscalculation of the load distribution equilibrium, which is required to be maintained during the undocking procedure of a vessel.