First attempts to locate missing Malaysian Airlines Flight 370 using a robotic submarine have ended unsuccessfully after its mission had to be cut off early. The Bluefin-21 was deployed to the southern Indian Ocean to detect wreckage signals based on where "black box" flight recorders were identified, but it exceeded its operating limit. It was supposed to do a 24-hour mission Monday, but completed only six. The U.S. Navy said no objects or data of interest were found during that time. Last week, four acoustic signals believed to be from the missing flight were detected, but no other signals have been identified since April 8. The flight itself has been missing since March 8, after leaving Kuala Lumpur carrying 239 passengers. The submarine is expected to be deployed again Tuesday if the weather holds up.