ABE, a nomadic adventurer that plumbed the world's oceans on its own, forever changing the way scientists explored the seafloor, was lost at sea March 5 off southern Chile. The autonomous underwater vehicle was about 16 years old and in the off-seasons was stored in Woods Hole, Mass.

ABE had been enlisted after a period of semiretirement to help researchers look for hydrothermal vents at the Chile Triple Junction, the meeting point of three tectonic plates. It was most likely destroyed by the implosion of a pressure housing or buoyancy sphere under enormous water pressure at a depth of about 10,000 feet, said Dana Yoerger, a senior scientist at Woods Hole Oceanographic Institution and one of the engineers who built ABE in the early 1990s with a $1.1 million development grant.

Yoerger, speaking from the research vessel Melville, which was using ABE to survey the seafloor, said two acoustic transponders aboard the craft had failed simultaneously. "For both to die at exactly the same time means probably something very bad and very violent happened," he said. The implosion of one pressure structure would have generated a shock wave that would have destroyed others, rendering the craft inoperable and consigning it to the seabed forever.

With its two bulbous pods attached to a cylindrical main body by V-shaped struts, ABE, short for Autonomous Benthic Explorer, resembled a pillowy Starship Enterprise and was a familiar sight on expeditions by Woods Hole scientists and others. It was one of the earliest autonomous underwater vehicles developed for civilian use, and one of the most successful. Its last dive was the 222nd of its career, which began in 1994.

Before ABE, underwater research craft were either small crewed submarines or unmanned vehicles tethered to a research ship by cables that provided power, communication and control. Being autonomous - it relied on batteries and programmed instructions, having only limited communications capabilities - ABE could work faster, cheaper and in more places, Yoerger said.

It was the first autonomous underwater vehicle to map a mid-ocean ridge and find hydrothermal vents, successes that had an enormous influence on researchers. "ABE's early work won most scientists over," Yoerger said. "This was a legitimate tool - it was worth the money, it was worth the risk."

He added, "ABE was the vehicle that showed the scientific community that all that was possible."

Chris German, a Woods Hole senior scientist who is on the Chile expedition, said there had been plenty of false alarms in the past when ABE had lost contact with its ship. "But this time," he said, "it really was the bad news we'd always worried about."

But the expedition, which began Feb. 24 and was to end Wednesday, continued, German said. "You're stuck at sea and you can't just cry and go home," he said. "So you figure out what's the best you can do with what's available."

That has involved using more conventional equipment to sample the water for other evidence of hydrothermal events, compiling data that can be used when researchers come back.

ABE is survived by a new generation of autonomous underwater vehicles with improved range, speed and sensing capabilities. Its most direct descendant is Sentry, developed at Woods Hole. It was Sentry's unavailability for the Chile expedition that led the researchers to bring ABE out of storage.

Yoerger said he had tried not to become too emotional about the loss of ABE, particularly given the human suffering nearby in Chile from the recent earthquake.

"This is aluminum, glass and silicon," he said. "We can build a new one."

Still, he said, there had been some trying moments.

"The most difficult one was writing the e-mails to my children and grandchildren telling them that their robotic friend was gone," Yoerger said.