U.S. Navy's future attack sub will need stealthy advanced propulsion, controls for multiple UUVs

Megan Eckstein, U.S. NAVAL INSTITUTE NEWS
9 March 2016
The Navy won’t begin buying its next-generation attack submarine until 2034, but researchers are already hard at work on two key components of the SSN(X) program: an advanced propulsion system for quieter operations, and the ability to control multiple unmanned underwater vehicles at once for extended influence.
These attack boats will operate through the end of the 21st century and perhaps into the 22nd century – and
Program Executive Officer for Submarines Rear Adm. Michael Jabaley believes there will still be a place for submarines in naval operations as long as the boats can keep up with changes in the operating environment.
“There’s been a lot of discussion about the future of submarines and the future of stealth and the future of anti-submarine warfare – and we take all of that into account and still firmly believe there’s a significant role for the submarine in the United States Navy well into the heart of this century and beyond,” Jabaley told USNI News in a March 3 interview.
“Now, that said, there are a lot of things that are happening that require some fundamental changes to what we consider an attack submarine to be. And some of it we’re already doing” as the office works through the design of the upcoming Ohio Replacement Program ballistic missile submarine.
To keep up with ever-improving sonar systems, the ORP will have an electric drive system.
“It’s still got a nuclear reactor, it still uses that reactor to generate heat and generate steam, but ever since we went to the nuclear reactor we’ve used that steam to drive turbines to generate electricity and turbines to generate main propulsion,” he said.
“This is one area where the significant improvements in stealth, quieting and sonar performance have gotten us to the point where we felt that in order to make the ship survivable over its entire lifespan we had to get away from those gears and pinions and reduction gears, because no matter how well you make them, they’re still heavy pieces of metal turning each other, and that generates a noise you just can’t completely quiet. So going to an electric drive system – still you’d have turbines to generate electricity, but now instead of turning gears and pinions and reduction gear, you’re turning an electric motor. So that’s a significant advance in quieting.”
SSN(X), then, could have either a similar electric drive to stay as quiet as possible, or a new advanced propulsion system that does not exist today, Jabaley said. He is already challenging the research and development communities in and outside of the Navy to tackle his propulsion problem to help these future attack subs remain as stealthy as possible regardless of whatever advances in anti-submarine warfare the next several decades bring.
“I’m not just talking about the propeller or propulsor, it’s the whole propulsion system from power generation to motion through the water,” he said.
“How am I going to get beyond the limitations of a rotating set of blades and the unavoidable noise that I just can’t get below? At this point there are no bounds on what I want people to be thinking about. I’m not the smart guy – they’re the smart guys, come tell me what the next submarine is going to look like and why, and then we’ll figure out is that achievable, can we develop the technology to get there, and then do the trade analysis – here are the benefits it brings, here’s the cost it requires versus what we’ve done in the past.”
An advancement in propulsion would, hopefully, bring about defensive advantages, making the submarine harder for a potential adversary to locate. To boost the submarine offensively, Jabaley said deploying multiple UUVs simultaneously would be a must for SSN(X).
“We have done a reasonably good job of designing UUVs that can be deployed using existing interfaces, we’ve deployed them out of torpedo tubes, out of the 3-inch countermeasure launcher, out of the trash disposal unit, but it’s almost always one at a time and limited time and it requires the entire focus of the ship to do that at that time. We’ve got to get beyond that,” he said.
“So the SSN(X) has to have UUVs as a key part of expanding its reach so the affected domain of that submarine grows from just the immediate area that its sensors interact with to something much much larger.”
Jabaley said this vision would take advances in command and control to accommodate working with multiple vehicles at once, communication, data relay, and even energy – with UUVs constantly deploying, they would need to be quickly recharged, which could take place by bringing the vehicles back to the submarine or by directing them to chargers on the seafloor.
“This new submarine is going to have to lock into a system that allows its impact to be felt in a much much greater sphere than we have now,” Jabaley said.
As the Navy works towards that goal, there may be an opportunity to test incremental advances in future Virginia-class subs instead of waiting for the SSN(X) program to start. The Virginia-class attack subs have been built in blocks – Block III lowered the cost per boat to about $2 billion, and the current Block IV tackled total ownership costs by eliminating the need for a maintenance period and adding an additional deployment in its place. Block V, which will begin in Fiscal Year 2019, will insert the Virginia Payload Module to help mitigate the reduction in firepower when the four SSGNs – which carry 154 Tomahawk missiles each – retire in the mid-2020s.
Blocks VI and VII, though, remain undefined still in terms of the improvements they will bring to the class, Jabaley said. These boats may present an opportunity to start introducing more advanced UUV operations ahead of the major shift SSN(X) will bring.