An Australian naval vessel carrying an underwater drone set off yesterday on its second mission to scan the Indian Ocean where the longest sonar "ping" thought to be from Malaysia Airlines Flight MH370 was heard last month.

The Ocean Shield will launch the Bluefin-21 submersible in the area where a signal was heard for two hours on April 5, 1000 miles northwest of Perth.

More than 24 countries have helped in the hunt for the Boeing 777 that vanished shortly after taking off from Kuala Lumpur for Beijing with 239 people on board.

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