The Defense Advanced Research Projects Agency (DARPA), America’s resident defense technology agency, is exploring new ways to track and defeat submarines.

This week BAE Systems announced that DARPA awarded it the first phase of its Mobile Offboard Clandestine Communications and Approach (MOCCA) program. The MOCCA program seeks to combine the advantages of active and passive sonar detection to give U.S. submarines a comparative advantage over increasingly capable Russian and Chinese vessels.

Submarines have traditionally relied on passive sonar that simply listens to sounds to try to locate adversary submarines and surface ships. This is less effective than active sonar—particularly with the proliferation of increasingly silent diesel submarines—but does not give away the location of the submarine. By contrast, active sonar is more effective, bouncing sound waves off submarines and other ships or objects to detect and track them. The problem with active sonar, as one observer explains, “is it’s like shining a flashlight in a darkened room: it can find objects effectively, but gives away its presence and forfeits any pretense of stealth.”

The MOCCA program seeks to give submarines the advantages of active sonar without compromising their stealth. It does this by launching unmanned underwater vehicles that are equipped with bistatic sonar. Therefore, the UUV will use active sonar to detect and track enemy vessels and send their location back to the host submarine, which will be equipped with sonar receivers.

In soliciting bids for the program last year, DARPA summarized: “The objective is to achieve significant standoff detection and tracking range through the use of an active sonar projector deployed offboard a submarine and onboard an Unmanned Underwater Vehicle (UUV). The submarine will need the ability to coordinate the operational functions of the supporting UUV.”

One of the major challenges for the program is that communication links between the host submarine and UUV can’t be intercepted by hostile forces, which could compromise the location of the submarine. As DARPA put it when soliciting bids, “An ideal link would have a low probability of intercept and of exploitation and provide high link reliability. The MOCCA communications link cannot degrade submarine stealth.”

Another major challenge the program will have to overcome is that the small size of UUV makes it ill suited to be an active sonar projector. Although the MOCCA project is not expected to develop an actual UUV, DARPA said the sonar and communications payloads it does develop should work on a submarine-launched UUV with a maximum diameter of the UUV. It also noted, “The volume available for the projector is highly constrained which makes high-output transducer materials a necessity.” The vessel will also have to be extremely energy efficient, so that it can be out for long periods of time.

BAE Systems is expected to solve both of these programs during the first phase of the contract. “Phase 1 will advance MOCCA technologies from conceptual design through preliminary subsystem design,” is how DARPA explained the process.

This is not DARPA’s first foray into antisubmarine warfare (ASW). The defense technology organization is also running the Anti-Submarine Warfare Continuous Trail Unmanned Vessel (ACTUV). Pronounced “active,” the ACTUV program produced a 132-foot-long unmanned surface vessel called Sea Hunter that is currently being tested.

As Kris Osborn previously noted for the National Interest, “The ship is built to travel up to 10,000 miles while using sonar and other sensors to locate mines and even the quietest enemy submarines. The Sea Hunter’s high-frequency sonar can send acoustic ‘pings’ into the ocean before analyzing the return signal to determine the shape, size, speed and characteristics of any undersea enemy activity.”

ACTUV’s program manager Scott Littlefield has previously said that the overall goal of the project is “to build something very affordable which could probably be acquired in large numbers.” But, as Osborn noted, the Navy is now considering expanding the ship’s mission portfolio to include thing like surface-warfare missions, firing weapons and launching electronic attacks, all of which are likely to increase the costs of each ship.

DARPA’s self-described “singular” mission is making “pivotal investments in breakthrough technologies for national security.” During its existence, it has been behind some of the most important technological breakthroughs, including the early versions of what would become the internet. That it is now so focused on antisubmarine warfare demonstrates that America’s military is increasingly concerned about its ability to dominate the subsurface domain.

The most obvious challenger is China, which has been rapidly bolstering its submarine fleet and deploying quieter (and thus harder-to-detect) vessels. Already in 2015, Naval officials were conceding that China had more submarines than the United States, and by some estimates will have nearly twice as many attack submarines as America by 2029. Although many of its current subs are vastly inferior to their American counterparts, U.S. Navy officials have described some of its newer ones as “fairly amazing.”

DARPA’s interest in ASW is also a reflection of emerging technologies that are making even the quietest submarines increasingly vulnerable to detection, something that Bryan Clark outlined in a 2015 report for the Center for Strategic and Budgetary Assessments. In that report, Clark presciently noted, “The ability of large UUVs and submarines to conduct and coordinate operations will improve with the introduction of new weapon, sensor, and communication systems.” Now, DARPA is seeking to add small UUVs to the mix.

Zachary Keck is the former managing editor of the National Interest. You can find him on Twitter: @Zachary Keck.

Image: A Russian submarine is anchored on the Neva River in central part of the city of St. Petersburg, July 27, 2012. The submarine will take part in Navy Day celebrations on Sunday. REUTERS/Alexander Demianchuk