Even something as large as a jetliner isn't easily found. Massachusetts-based nonprofit Woods Hole Oceanographic Institution conducted the search for Air France 447 using a set of unmanned subs, but it wasn't until a third search trip and 109th dive that the wreckage was found.

"It can be challenging, especially when you don't have a good map of the sea floor, which I think is how they're operating," said Mike Purcell, principal engineer with Woods Hole. "I'm certainly very glad when we were doing the Air France search, we didn't have the scrutiny these guys do."

Crews in such missions spend weeks at sea, constantly running searches, downloading and sifting through data, and troubleshooting problems that frequently arise.

"You're six days out of port; you can't call Radio Shack for help," Weller said.

If the submarine does find the Malaysia Airlines wreckage, a difficult search still could remain for the black box. After Woods Hole found the Air France debris in 2011, Phoenix, using a different type of submarine that more closely resembles part of a tractor, recovered flight recorders a month later. Crews take turns on 12-hour shifts, manning the vehicle from a tiny control panel inside a shipping container.

Phoenix, Woods Hole and Massachusetts company Hydroid Inc. are among the few players capable of exploring the ocean's depths. Jaffe said he expects that to grow, perhaps due to interest in oil and gas exploration, but companies like Phoenix are well positioned given their experience.

"I think it's only going to get more interest in the future, and their vehicles could be used for survey," Jaffe said. "From the oceanographic point of view, it's not a bad place to be."

Reuters contributed to this article.