June 25, 2025: China has followed the American example and developed an extra-large underwater drone or XLUUV. The Chinese version apparently carries four torpedoes or eight mines and is automated, with no crew on board. This drone is 12 meters long and 1.8 meters in diameter. Last year China publicly revealed its 50-ton UUV-300 unmanned drone submarine. This one was described as useful for reconnaissance and surveillance as well as installing naval mines without being detected. It is 28 meters long and 2.5 meters in diameter. It has a max speed of 18 kilometers an hour and a cruising speed of 8 kilometers. Endurance is 600 kilometers. It is relatively silent with an acoustic signature under 140 decibels. China appears to have tested several different underwater drone designs before choosing their new XLUUV and smaller UUV-300.

The U.S. Navy believes robotic subs carrying mobile mines would be an effective new ASW asset because the U.S. has already developed some of the new ASW technology needed for this. This includes Unmanned Underwater Vessels/UUVs and mobile mines. Over a decade ago the navy adopted civilian underwater UUVs used for monitoring the oceans and has been using them to do that as well as collect data useful for wartime submarine operations. With a growing number of civilian and military customers, American UUV developers and manufacturers have been coming up with new ocean research UUVs that also have military applications. The latest example of this is the new class of XLUUVs with the ability to go deeper, carry a cargo bay for other research gear to be stored and deployed from, and operate autonomously for up to six months. The first of these XLUUVs was the Echo Voyager, which Boeing developed from a research project and had the first one ready for testing in 2016. The tests were successful and have involved more complex and completely autonomous operations. In 2019 the navy ordered four militarized Orca versions of the Echo Voyager for $11 million each.

Both models are diesel-electric powered autonomous subs that are 16 meters long with a payload compartment 9.1 meters long and 2.6 meters in diameter which is inside the pressure hull. Propulsion is by battery-powered electric motors and diesel generators to recharge the batteries when on or near the surface. This XLUUV has no topside sail and can stay underwater for days at a time because there is no crew on board to sustain. While submerged these UUVs can move at 14 kilometers an hour and have sufficient generator fuel to travel 12,000 kilometers.

The main difference between Echo Voyager and Orca is that Echo Voyager is built to dive to 3,400 meter depths. Orca does without that but adds additional passive sensors and signal processing computers to detect other submarines or surface ships. There is also an underwater communications system for arming the dozen Hammerhead mobile mines Orca is designed to carry and place on the ocean floor in areas like the South China Sea. These Hammerhead bottom mines carry a Mk 54 lightweight torpedo, which is normally carried by ASW helicopters and aircraft. Mk 54 has a range of ten kilometers and a guidance system that is regularly updated. Hammerhead is being used in a similar fashion to a larger version of this used during the Cold War that deployed a larger Mk 48 torpedo. Hammerhead is an encapsulated system equipped with passive sensors to detect and identify submarines and surface ships and attack specific types of targets, like diesel-electric subs larger than Orca.