Earlier this month, the El Faro cargo ship mysteriously disappeared as it approached the Bahamas, where it collided with the 125-mph winds and 50-foot seas of Hurricane Joaquin. The US Coast Guard believes the ship sank after taking on water and seeing its engines fail, though a clearer picture likely won't emerge until authorities recover its voyage recorder. On Wednesday, six days after losing contact with El Faro, authorities called off the search for the 33 people that were aboard.

It's not unheard of for cargo ships to sink — 49 sank or were submerged in 2014 — but as The Atlanticreports, it's very rare for a ship of El Faro's size to simply disappear, without sufficient warning to evacuate crew members. And in cases where accidents do occur at sea, human error is usually to blame.

That has spurred some groups to develop more autonomous technologies that would all but remove humans from the equation. Such "drone ships" would be remotely piloted by onshore captains, but all the onboard operations that crew members currently carry out, like navigation and power management, would be handled by computer systems. Advocates of the technology say it would make shipping safer, less expensive, and more environmentally friendly. But the proposals have been met with skepticism from shipping labor unions, and there are major regulatory hurdles that still need to be cleared.

"the development will not happen overnight."

"We see the industry having oceangoing, big unmanned ships in the future, but the development will not happen overnight," says Oskar Levander, head of innovation at the marine division of Rolls-Royce Holdings. Rolls-Royce began developing unmanned ship technology in 2013, and last year completed a virtual reality command center that serves as a prototype for its vision. The company believes captains will eventually be able to remotely control hundreds of ships from similar centers onshore, in the same way that military drones are piloted today.

The idea is that within the coming decades, nearly all of a ship's functions would be carried out automatically. Vessels would be able to navigate their way across oceans, and would automatically manage and optimize the power they use. Humans would still need to conduct maintenance and repairs when the ship comes into port, but Levander says some of the more basic operations could be handled by robots.

Today, the "technological building blocks are all in place," Levander says, though he estimates that Rolls-Royce is still 10 to 15 years away from deploying a large drone vessel in international waters. The company is still working to determine how best to combine and display the data gathered by a ship's sensors — including lidar, radar, and infrared — and is honing its automatic object detection systems. There's also the question of whether the crewless ships of the future would be safeguarded against hackers and other cyberattacks.

Unmanned ships are still illegal under global regulations

But Levander says the biggest obstacle is regulatory, rather than technical — a reality shared by road-going autonomous vehicles. International regulations currently require all ships to have a crew aboard, and autonomous systems would have to meet strict rules on safety and collision avoidance. But there is growing interest in the area. The European Union has funded a $4 million study to develop autonomous ship concepts, and the shipping research firm DNG VL last year revealed its own designs for a crewless cargo ferry.

Rolls-Royce believes the technology's benefits will eventually push the industry forward. Shipowners would spend less to maintain their crews, and the lower weight resulting from the elimination of crew bunks, latrines, and kitchens would bring down fuel costs. Advocates also say the technology would put fewer people in danger; in 2012, an estimated 75 to 96 percent of all marine casualties were attributed to human error, according to a study from the insurance group Allianz. Workers wouldn't be at risk of attacks from pirates, and instead of spending months at sea, they could live at home and commute to port to service incoming ships.

Until regulations are changed to allow for uncrewed ships, Rolls-Royce is focusing on smaller trials outside of international waters. The company hopes to demonstrate its technology on a small coastal ship by the end of this decade. Levander also stresses that the transition to fully autonomous ships won't be automatic. Instead, he envisions crew sizes gradually diminishing (as they have for several decades already) until the technology proves safe and viable.

Not surprisingly, the proposals have been met with opposition from some shipping unions. "It cannot and will never replace the eyes, ears, and thought processes of professional seafarers," Dave Heindel, of the 600,000-member International Transport Workers' Federation, told Bloomberg in February 2014.

"Seafarers have always been very good at adapting to technological change."

But others have adopted a more circumspect stance. "We're not, and shouldn't be thought of as Luddites," says Andrew Linington, director of campaigns and communications for Nautilus International, a trade union representing more than 22,000 maritime professionals in the Netherlands, Switzerland, and the UK. "Seafarers have always been very good at adapting to technological change."

Linington says many seafarers are concerned about what autonomous technology will mean for their jobs, and are worried that they won't receive adequate training to adapt to it. But others acknowledge that the change could improve safety and bring opportunities for new high-skilled jobs. "The reality is, we all know technology marches in an inexorable way, and it's hard to swim against the tide," Linington says. "We'd much prefer to try and work with it." (His union isn't alone; on the highway, freight drivers face similar disruption from the advent of self-driving semi trucks.)

Levander points out that humans will likely never be completely divorced from shipping operations. Companies would still need highly skilled captains to helm the control room, and cruise ships or vessels carrying dangerous cargo would likely keep a small crew onboard. And there are always unforeseen circumstances that will require humans to make quick decisions.

But he's confident that the transition is inevitable. "If you look at society, every single industry is trying to become more efficient, to do more with less," Levander says. "Why would shipping not try to do the same thing?"