The kickable "robotic mule," also known as AlphaDog or LS3, created by Alphabet-owned Boston Dynamics under a contract with DARPA, has proved too loud to fight alongside the US Marines. Following an extended test period during the "Rim of the Pacific" military exercise last year, the project has been suspended.

The Legged Squad Support System (LS3) was created to carry heavy equipment for the Marines during marches, bearing a load of up to 400 pounds (180kg). This would have provided much-needed relief for the fighters: the average soldier is supposed to carry no more than 72 pounds (32kg) when marching and 48 pounds (22kg) when fighting, but paratroopers fighting in Iraq in 2003 carried up to 101 pounds (46kg). In total, about $42 million (£28 million) was awarded to Boston Dynamics to develop the robodog.

Unfortunately for those over-laden soldiers, however, the military exercise clearly showed that LS3 in its current state is not suitable for real-life use by the US Marine Corps, Military.com reports.

"As Marines were using it, there was the challenge of seeing the potential possibility because of the limitations of the robot itself," said Kyle Olson, a spokesman for the Marine Corps Warfighting Lab. "They took it as it was: a loud robot that's going to give away their position."

The robotic mule is fitted with a petrol-powered engine that produces significant noise when working; some have likened it to the sound of an angry swarm of bees. Under the same contract with DARPA and the Warfighting Lab, Boston Dynamics built a quieter, electrically powered and hydraulically actuated robot known as Spot. However, the mule's little brother could only carry about 40 pounds (18kg), which is clearly not enough for the marines.

"I see Spot right now as more of a ground reconnaissance asset," captain James Pineiro, the Ground Combat Element branch head for the Warfighting Lab, told Military.com. "The problem is, Spot in its current configuration doesn't have the autonomy to do that. It has the ability to walk in its environment, but it's completely controller-driven."

In addition to that, it is unclear how both robots could be repaired if they break down on the move.

For the time being, both the LS3 and Spot projects have been put on hold. The developers don't plan any future experiments or upgrades unless the Marines give the Warfighting Lab a new contract. Instead of that, the lab is experimenting with unmanned vehicles, including drones for reconnaissance and medical resupply purposes.