The sea was heaving, the skies gray. The captain of the research ship was worried about the weather.

About 120 miles off the coast of Spain, three Rutgers University scientists had a narrow window of opportunity to find and retrieve their prize—an 8-foot, torpedo-shaped yellow robot that they had launched seven months earlier off the coast of New Jersey.

They could grab it and learn from it, or in the rough seas accidentally ram it and sink it.

After an hour of pitching in the 20-foot waves, the shipmates let out a cheer. Having spent 221 days at sea on a voyage of 4,604 miles, the robot dubbed Scarlet Knight was safely aboard.

With that came the completion of a mission that made oceanographic history.

Not only was the robot—an underwater glider—the first of its ilk to cross the Atlantic, a mission supporters compared to Sputnik and Charles Lindbergh’s solo flight. “She,” as the glider is referred to on her Facebook page, also had collected valuable data, finding eddies of current in unexpected places.

The eddies, said Scott Glenn, the Rutgers professor who led the mission, “are the ocean’s weather. It’s the equivalent of atmospheric storms. And all these add up to give us our climate.”

Underwater gliders such as the Scarlet Knight are ushering in a new frontier of oceanography, researchers say, one that can help solve the riddles of weather and climate change plus provide data to manage fisheries and guide shipping.

Research ships are the traditional way to sample the planet’s oceans, but they’re expensive and cumbersome, said Dean Roemmich, a researcher with the Scripps Institution of Oceanography in San Diego.

Satellites beam back data, but only from the surface.

Roemmich works with another project, dubbed Argo, which employs 3,000 buoys worldwide, about 180 miles apart, to sample the water column. But they can only drift.

The glider, loaded with data sensors, can be directed.

“We are data poor for understanding how the ocean operates, and this is going to give us the capability to understand this much better,” said Richard Spinrad, assistant administrator of the National Oceanic and Atmospheric Administration in Silver Spring, Md.

“If we can go across the Atlantic, we can go just about anywhere with these.”

For its long, solo flights, the glider needs to be a power miser.

The Scarlet Knight requires the energy of just three Christmas tree lights to run, but stretch that out over a seven-month journey and the glider had to be crammed with 450 lithium C-cell batteries, making up half its 134 pounds.

Nearly 40 percent of that energy is dedicated to a propulsion system that, instead of using a power-hungry propeller, makes use of changes in its buoyancy.

When its onboard computer instructs the glider to submerge, a piston in the nose draws back, taking in about a cup of water. Even that small amount is enough to make the nose sink.

As the glider descends, its wings translate the downward motion into forward glide.

At the bottom of the programmed descent—as deep as 600 feet—the piston pushes the water out, the nose tilts up, and it all happens in reverse.

So it “flies,” as they say, in a sawtooth pattern, at just over half a mile an hour.