The Bluefin 21, the Artemis autonomous underwater vehicle (AUV), is hoisted back on board the Australian Defence Vessel Ocean Shield after a successful buoyancy test in the southern Indian Ocean as part of the continuing search for the missing Malaysian Airlines flight MH370 in this picture released by the U.S. Navy April 4, 2014. Malaysian police have ruled out involvement of any passengers in the disappearance of a missing jetliner, while Australian officials warned bad weather and a lack of reliable information were impeding efforts to find wreckage from the plane. Up to 10 planes and nine ships from a half dozen countries on Wednesday scoured a stretch of the Indian Ocean roughly the size of Britain, where Malaysia Airlines Flight MH370 is believed to have crashed more than three weeks ago. REUTERS/U.S. Navy photo by Mass Communication Specialist 1st Class Peter D. Blair/Handout via Reuters The U.S. military has committed $7.3 million thus far to the search for missing Malaysian Flight 370, with about half of the total spent on an unmanned submersible, Pentagon officials said Wednesday.

The $7.3 million figure included operations of the ships, planes, helicopters and sensors employed in the hunt for the Boeing 777 airliner from March 8 through April 8, said Army Col. Steve Warren, a Pentagon spokesman.

There were no plans in the works to ask the Malaysian government for re-imbursement, Warren said.

Last month, Pentagon officials said that $4 million had been set aside to search for the plane. The increase to $7.3 million appeared to come entirely from the $3.6 million that Warren said was spent to operate a Bluefin-21 unmanned submersible made by Bluefin Robotics.

The Bluefin robot, equipped with side-scanning sonar, multi-beam echo sounders and cameras, and 10 civilians to operate it were sent to Perth, Australia, under contract late last month.

The Navy has been using P-8 Poseidon surveillance aircraft to search for debris trails from the missing plane at a cost of $4,000 per hour to operate each plane, Warren said.

In recent days, several search ships have reported picking up possible pings from the black boxes of the plane that disappeared on a flight from Kuala Lumpur, Malaysia, to Beijing with 239 aboard.

The Australian Navy ship Ocean Shield, using the U.S. Navy's TPL-25 Towed Pinger Locator System, reported Tuesday on picking up at least two more underwater signals that may have come from the black boxes.

The Ocean Shield was attempting to get a better fix on the location of the sounds before sending the Bluefin-21 below in waters more than 14,000 feet deep off Australia's west coast, said Angus Houston, the head of a joint agency coordinating the search.

-- Richard Sisk can be reached at richard.sisk@monster.com