A combination of cutting-edge science, dogged analysis and simple luck prompted searchers to focus the hunt for Malaysia Airlines Flight 370 underwater, just days before the plane's black box recorders were expected to fall silent.

Authorities got a first look at the sea floor Tuesday in an area that they believe is the jet's likely location, without detecting any wreckage. Hopes rest on a remote-controlled submersible from the U.S. Navy, which is seeking the first visual confirmation of wreckage that could lead investigators...