Four robots have set a new distance world record, swimming more than 3,200 nautical miles (5,926km) across the Pacific Ocean.
The drones are taking part in a project to gather data about the composition and quality of sea water.
Built by US-firm Liquid Robotics, the PacX Wave Gliders are expected to cover 9,000 nautical miles (16,668km) by their journey's end.
The first leg of their voyage from San Francisco to Hawaii took four months.
The robots are designed to reach previously inaccessible areas of the ocean and gather data on how acidic the water has become and the shrinking size of fish stocks.
The previous Guinness World Record for the longest distance covered at sea by an unmanned device was 2,500 nautical miles (4,630km).
"I have no doubt new ocean discoveries, insights, and applications will emerge from the PacX data set,"said Edward Lu, chief of innovative applications at Liquid Robotics.
Thegliders were launchedfrom the St Francis Yacht Club at San Francisco harbour on 17 November 2011.
Each robot is composed of two halves: the upper part, shaped like a stunted surfboard, is attached by a cable to a lower part that sports a series of fins and a keel.
To move they do not use fuel but instead convert energy from the ocean's waves, turning it into forward thrust.
Solar panels installed on the upper surface of the gliders power numerous sensors that take readings every 10 minutes to sample salinity, water temperature, weather, fluorescence, and dissolved oxygen.
After a short stopover in Hawaii, the quartet will split.
Two drones will continue to Japan, crossing the Mariana Trench en-route - the deepest place on Earth.
The second pair will swim to Australia, passing the equator.
Researchers expect both "teams" to reach their destinations by late 2012 or early 2013.