The US military has reportedly shelved development of its robotic pack mule — the Boston Dynamics-built Legged Squad Support System or LS3. According to a report from Military.com, there are no "future experiments or upgrades planned" for the mechanical beast of burden, with the program in need of new contracts or support from senior military figures before it can be resurrected. And the reason for this parting of ways? LS3 was apparently too noisy to make a good soldier.

"They took it as it was: a loud robot that's going to give away their position."

"As Marines were using it, there was the challenge of seeing the potential possibility because of the limitations of the robot itself," Kyle Olson, a spokesperson for the Marine Corps Warfighting Lab which helped develop LS3 along with the Defense Advanced Research Projects Agency (DARPA), told Military.com. "They took it as it was: a loud robot that's going to give away their position."

Noise has always been a bit of a problem for Boston Dynamics' robotic quadrupeds. LS3's predecessor BigDog was powered by a two-stroke go-kart engine, and a contract in 2013 to develop the Legged Squad Support System (reportedly worth almost $10 million) specified that it needed a quieter method of propulsion as well the ability to better resist gunfire.

Over the course of its development, LS3 was given updates to make it more autonomous, able to automatically follow humans and even respond to basic voice commands like "follow," "sit," and "stay." But, it seems it never really became all that quiet. In videos of the barrel-chested robot in action during military trials last summer, it sounds as loud as a sit-on lawnmower — definitely not the sort of companion you'd want bumbling alongside you on a nighttime patrol.

Boston Dynamics — which was bought by Google in 2013 — did attempt to remedy these problems by building a smaller, electric-powered version of the robot named Spot. But, says Military.com, this version had to be steered by a driver at all times and could only carry around 40 pounds of equipment — far less than the LS3's capacity of 400 pounds, and not enough to fulfill the role of pack mule.

It's not clear, though, whether or not we've seen the last of this breed of robotic quadruped. The Marine Corps say it's learned a lot about autonomous technology from the project, and the machine's self-balancing capabilities have always seemed impressive. Perhaps if suitable engine technology is found in the future these robots will come high stepping back into fashion. Who knows, we might never even hear them coming.

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