“Underwater data links are a relatively mature technology. The challenge here is to create one that can provide high bandwidth if the UUV needs to send data to the submarine and can also be hard for an enemy to detect,” said Bryan Clark, a retired submariner and former aide to the Chief of Naval Operations, how the Center for Strategic & Budgetary Assessments. (Clark wrote an intriguing study on underwater communications). The crucial question is how much bandwidth you want, which in turn depends on what, exactly, you want the drone to do. There are two basic approaches, Clark told me:
- The unmanned underwater vehicle has an active sonar transmitter, but only the manned submarine has a receiver. This basically splits the sonar in two. The UUV is just sending out the ping, not listening for the echoes. That means it’s not collecting any data, which means it doesn’t need to transmit much. This is the stealthier approach — but it forgoes the opportunity of using the UUV as a second sensor platform to look at things from a different angle.
- The UUV has both a sonar transmitter and a receiver. The submarine’s passive sensors can still listen for the echoes from the UUV’s pings, but now the UUV is listening too, providing a second chance to pick up faint signals and a second perspective to triangulate a signal’s source. The problem is now the UUV has to transmit all this information back to the manned submarine. This approach is more likely to see the enemy coming, but it’s also more likely to be seen.
“If the UUV just transmits active sonar and other platforms listen to the reflections form the sonar, the datalink only needs to be able to control the UUV and provide feedback on its location,” Clark said. “If the UUV is also acting as a sensor, much more bandwidth is needed, (and) as bandwidth goes up, the required power level probably rises and could make the link more detectable.”
Clark still firmly believes underwater drones are central to the future of naval warfare: He just never said developing the technology or the tactics would be easy. “Overall, the idea of using UUVs as adjuncts to submarines or surface ships in Anti-Submarine Warfare to be sensors…is a good one,” he told me. “The key is coming up with tactics and applications where they offer better performance than the traditional approaches we use today.”