US submarine hunt for MH370 'fails' as search area proves 'too deep'

An autonomous underwater vehicle sent into the Indian Ocean to search for evidence of missing Malaysian Airlines flight MH370 hit hurdles and hauled back from its first mission.

The US Navy's underwater drone Bluefin-21 was deployed from Australian Defence Vessel Ocean Shield to begin the search at the bottom of the Indian Ocean search zone, off the coast of Western Australia.

According to the Sydney Morning Herald, however, it returned six hours after its first 16-hour mission because it had reached its maximum operational depth of 4.5km, the Joint Agency Coordination Centre said.

The Bluefin-21 was meant to cover an area of 40 square kilometres on its first day underwater, using side sonar to create a 3D image of its surrounds, the report said.

However, the Bluefin-21 is expected to redeployed later on Tuesday, 'when weather conditions permit', JACC added.