The HMAS Dechaineux was just 20 seconds from sinking irretrievably to the bottom of the Indian Ocean with 55 sailors onboard while off Western Australia in February 2003, the Weekend Australian said, quoting crew members.

According to the report, the submarine began flooding when a sea water hose in the lower engine room failed while it was at its deepest diving depth.

The deepest diving depth, as well as the depth at which the submarines now operate, is classified information.

"There was a loud bang and something hard flew past my head," Able Seaman Geordie Bunting, who nearly drowned when the room flooded, told the paper.

"Then the water flooded in and I got tossed around like in a washing machine.

"Another five seconds and we would have been in big trouble... another 10 and you have got to question whether we could have surfaced."

Former commander of the navy's submarine fleet, Mike Deeks, told the paper that the flooding was "very serious, significant."

"We were talking seconds, not minutes," he said.

According to the report, the submarine had taken on so much water it was slow to resurface. If the flooding had not been stopped in time, the vessel would have been smashed by water pressure before it hit the seabed.

"It would have been like crushing an empty Coke can in your hand," Bunting said. "We were too deep to hit the bottom alive."

The paper quoted an unnamed senior crew member as saying the accident could have caused something "completely catastrophic."

"If it had been any worse, we wouldn't have got up, and if our propulsion system had failed we wouldn't have made it. We were probably only 20 seconds away (from death)."

The accident prompted the navy to reduce the depth to which its fleet of Collins-class vessels dive, the report said, without naming its source.

The submarines are among the nation's most valuable military assets.

Despite extensive testing, the navy has never been able to find a fault with the sea water hoses and they are still used, the report said.

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