1. Several rescue ships were searching the waters, and submersible craft had been deployed.

2. Researchers at MIT are working on submersible machines that could use ultrasound to find drugs hidden on ships.

3. However, the newly detected signals did not narrow the search area enough to dispatch a submersible vehicle to search for wreckage.

4. An intensive search of the seabed in that area by an unmanned submersible has not turned up any sign of the plane.