New Delhi, Jan. 16: The Indian Navy has contracted a US firm to get a toppled warship upright for about Rs 20 crore.

The US-based firm, Resolve Marine Engineering, also salvaged the INS Sindhurakshak, the Indian Navy submarine that sank in the Mumbai Naval Dockyard on August 14, 2013, taking with it the lives of 18 crew.

It took nearly a year to salvage the submarine. To little or no avail. It cannot be used for the purpose it is meant for: waging undersurface warfare. But the navy has still not decommissioned it.

Unlike that submarine, the INS Betwa, a Brahmaputra-class frigate weighing 3,850 tonnes, is still capable of being battle-worthy, the navy believes.

In December, the Betwa "toppled" on its port (left) side while being undocked during a refit.

A navy officer said the technology involved in getting the ship upright was available in the region only with Resolve.

A toppled ship is almost unheard-of.

The officer explained that the salvage team would use sponsons - supports - on the ship's flank that is now horizontal in the drydock. While the sponsons lift the ship partly, the drydock would be flooded gradually to make the vessel buoyant.

The ship toppled because of unequal weight distribution when it was on supports. The officer said the salvagers would distribute weight, while the vessel is buoyant, in such a way that at one point it would set itself right.

This is an optimistic view, the officer admitted. "Expect trial and error and a few accidents," he said.

The frigate was commissioned in the year 2004. It went into refit in April last year. When it toppled, two sailors were killed and 14 others injured. But navy sources say that much of a delicate machinery had been removed before repairs to the underwater hull had begun.