PERTH, Australia — Four weeks after the Malaysia Airlines jet vanished, two ships deployed sound locators Friday in the southern Indian Ocean in a desperate attempt to find the plane’s flight recorders before their signal beacons fall silent.

Officials leading the multinational search for Flight 370 said there was no specific information that led to the underwater devices being used for the first time, but that they were brought into the effort because there was nothing to lose.

The air and sea search has not turned up any wreckage from the Boeing 777 that could lead searchers to the plane and perhaps its flight data and cockpit voice recorders, or “black boxes.”

The recorders could help investigators determine why the Malaysia Airlines plane, which disappeared March 8 while en route from Kuala Lumpur to Beijing with 239 people aboard, veered so far off-course.

Beacons in the black boxes emit “pings” so they can be more easily found, but the batteries only last about a month.

Two ships with sophisticated equipment that can hear the pings made their way Friday along a 150-mile route investigators hope may be close to the spot where officials believe Flight 370 went down.