A submarine is joining the search for the missing Malaysian airliner.  The sub is joining a search crew of nearly two dozen ships and planes that are racing against time to find clues to the whereabouts of Malaysia Airlines Flight 370. 

Experts say the batteries in the plane's black box will fail in the next few days. The device is designed to ping for 30 days but the plane disappeared more than three weeks ago. 

The transcript of the final communication between the passenger jet and air controllers doesn't provide any answers as to what happened to the plane. The transcript shows the final transmission said "Good night Malaysian three-seven-zero" and not "All right, good night" as was originally reported. 

Malaysian Airlines Flight 370 is believed to have gone down somewhere over the Indian Ocean last month, but there's still no sign of wreckage. Officials believe all 239 people on board were lost.  The focus of the massive search has shifted since the plane first disappeared from radar.

More than a dozen countries are devoting manpower and equipment in hopes of finding any sign of the missing Boeing 777.