Run Silent, Fast and Undetectable – US Navy Submarines

An old 1955 movie was called “Run Silent, Run Deep”, about the US Navy’s submarine service in WWII. Our subs today are quite different and as you will see, a new movie might be named “Run Silent, Run Fast, Invisibly”. Subs today go faster than you would imagine, quieter than anyone thought possible and – thanks to a contribution I made 15 years ago – they are now almost invisible. My small part had to do with the stealth aspects of subs. The exact nature of stealth technology is a secret and I, for one, will not give it away but I can tell you something about it. But first, I have to explain a little about the technology.

Imagine you have a very large bundle of sewing needles. Tens of thousands of them. Now imagine you can set them all upright, with their pointy ends pointing up and pushed together as close as they can get. If you then looked down on those pointy ends, it would look very black. The reason is that the light on the sides near the points reflects inward and keeps reflecting as it bounces further and further down into the mass of needles. Officially, this is called, “the angle of incidence (the incoming light) equals the angle of reflection (the bounced light). With each reflection, a little of the light energy is absorbed and converted to heat. Because of the shape and angle of the needles, the light never reflects back outward thus making it appear to be totally black. In physics, this is called a “black body”.

This is essentially what stealth technology is like only at a microscopic scale. Aircraft are painted with a special kind of paint that has tiny but densely packed little pointy surfaces that act just like those needles. When radar hits the aircraft, the paint absorbs all of the radar’s energy and lets none reflect back to the enemy receiver. When no radar reflection is seen, it is assumed that there is nothing out there to be seen.

Sonar for subs works pretty much the same as radar but instead of radio frequency (RF) energy, it uses sound. Sound is emitted and a reflection is heard. This is called active sonar. Because subs are relatively noisy in the water, it is also possible to just listen for their noise and then figure out what direction the noise is coming from. That is called passive sonar. The props, engine noise and just the water rushing over and around the sub makes noise. The faster you go, the more these things make more and louder noise.

Despite their best efforts at sub design, even our subs create some sounds and they are, of course, going to reflect an active sonar bing when that is used. However, the US is the worlds best at creating very quiet subs. It is mostly because of the secret design of the props that are able to turn fast but not create cavitation – which makes a lot of noise underwater. Flush mounted hatches and even screw heads also make our subs quiet. In the 1960’s and 70’s, going over 15 knots under water was like screaming, “here I am”. In the 1980’s and early 1990’s, we could go up to 25 knots in relative silence. The latest subs – built or being built – can go over 35 knots and still remain mostly quiet.

That means that the enemy has to use active sonar to try to find them and that gives away the enemy’s position. At that point, they become easy targets.

Pushing a 400 foot long sub underwater at 35 knots is no easy chore but due to some amazing designs in the hull shape and the power plant and props, that is nowhere near the limit of the potential speed possible. Our subs could do as much as 85 knots underwater (that’s nearly 100 MPH!) but they would sound like a freight train and would create a wake large enough to be visible from space. Since stealth is the primary tactic of subs, that kind of speed was simple not reasonable….until now.

While I was at NRL, I presented a paper on how to create a totally quiet sub. Even if it were producing a lot of mechanical or hydroaction noise, my method would make it totally silent. More importantly, it would also completely hide the sub even from active sonar bings.

The advantages of this are significant. In a combat environment, going slow to keep the sub quiet also makes it linger in dangerous areas longer but going fast makes it easier to locate and track. Being able to launch weapons and then move very fast out of the area in total silence – even to active sonar – would be a game changer for submarine warfare.

Since I was a former pilot and worked in an entirely different department from the sub guys, the first reaction to my suggestion was “Yeah, Right – a flyboy is going to tell us how to make a sub quiet”. That was back in 1998. I recently found out that the latest sub, the Virginia, SSN-774, incorporates my design in an applied active acoustic quietness system that they now call Seawolf. When I contacted some old NRL friends and asked them about it, they were reluctant to talk about it until I started quoting my research paper from 1998. They said, “YOU wrote that paper!” Then they began to tell me the whole story.

It seems that my paper sat in files for six months before it was read by someone that understood and recognized it for what it could do. After a few preliminary computer models and some lab scale experiments, they were able to get funding for some major research and within a three months, they were proposing to incorporate the idea into the next class of subs. That was in early 2000. It was decided to incorporate the design into the last sub in the Seawolf class of subs – SSN-23, the USS Jimmy Carter. It proved to be effective but the SSN-23 was mostly a test bed for further development and a modified design was planned for the next class – the USS Virginia. After seeing how effective it was, the entire rest of the Seawolf class of subs was cancelled so that all the efforts could be put into the Virginia class with this new technology. My design was improved; named after the Seawolf class where it’s design was finalized and retrofitted into the Virginia before it was turned over to the Navy in 2004.

Soon after this discussion, I was invited to a party of the sub guys down near Groton. Since I was still at my Vermont residence, I figured, why not. I could go to my Canada residence right after the party. So last September; I flew my plane down to Elizabeth Field at the southwest end of Fishers Island. The sub guys from Groton had a nice retreat on the island at the end of Equestrian Ave. After I arrived, I was shown to a room upstairs in the large house and told to meet in the Great Room at 5PM. When I went down to the party, I got a huge surprise. I was the guest of honor and the party was being thrown for me.

It seems that they lost the cover page to my original 1998-research paper and never knew who wrote it. Several people at NRL had suggested that it was mine but they were sure that it had to have come from one of their own sub community guys but could never find the right one. When I sent someone a copy I had kept, they determined that I was the original author and deserved the recognition. It seems that my idea has actually been a game changer for the entire submarine warfare community in both tactics and strategy as well as hull design, combat operations, even weapons design. I was apparently quite a hero and did not even know it.

I enjoyed the party and met a lot of my old NRL buddies that were now admirals or owners of major corporations or renowned research scientists within select circles of mostly classified technologies. I got a lot of details about how they had implemented my idea and about some of the mostly unexpected side benefits that I had suggested might be possible in my paper. It was humbling and almost embarrassing to be honored for an idea that was now 15 years old and was mostly refined and developed by a host of other researchers. I began looking forward to getting on to my Canada retreat.

Two days later, I flew out for BC, Canada with a large handful of new contacts, renewed old contacts and lots of new ideas and details of new technologies that were being developed. I also ended up receiving several offers to do some research and computer modeling for some problems and developing technologies that some of the partygoers needed help on. I’ll probably end up with a sizable income for the next few years as a result of that party.

I suppose you’re interested in what exactly was this fantastic technology I designed way back in 1998 that has proved to be so popular in 2012. It was actually a pretty simple concept. Most techies have heard of noise-canceling headphones. They work by sensing a noise and then recreating an identical sounding noise with a phase shift of 180 degrees. When a sound is blended with the same sound but phase shifted by 180 degrees, what you get is total silence. This works very well in the confined and controlled environment of a headphone but was thought to be impossible to recreate in an open environment of air or water. I simple created a computer model that used a Monte Carlo iterative algorithm that quantified the location, intensity, lag time, and other parameters for an optimum installation on a sub. It took the super computers at NRL several hours to refine a design of placement, power, sensors and other hardware and temporal design aspects but when it was done, I was surprised at the degree of efficiency that it was theoretically possible to achieve. I wrote all this into my 1998 paper, mostly out of the hopes that my computer model would be used and I could get another project funded.

My paper included a reference to where and how to run my model on the NRL computers and eventually, it was used as their primary design optimization tool for what would later be called the Seawolf Acoustic Quieting and Stealth System (SAQ-SS). The actual modeling software I created and left on the NRL computers began being called SAQ, which got shortened to pronouncing it as “SACK”. As it developed and got seen by more people and they saw the side benefits on the whole stealth effect, it was called SAQ-SS, which evolved into “SACKSS”, then into SAQ-SaS and into SACK-SAS and was eventually called the “SUCCESS” system.

Those side benefits I keep referring to are worth mentioning. When an active sonar bing or sound wave front is detected by the SAQ system, it activates a hull mounted sound modulator that causes the hull itself to act as a giant speaker or transducer to initiate a response wave form that is 180 degrees out of sync from the incoming sound. This effectively nulls out the sound. The same happens for sounds created by the mechanics of the sub that is passed by conduction to the hull. In this case, the hull is modulated so that it completely absorbs any sounds that might otherwise pass through it to the water.

Another side benefit is that the SAQ system created the opportunity, for the first time, for the sub commander to “see” directly behind his own sub. In the past, the noise from the prop, the engine and the distortion of the water because of the prop wash; the rear of the sub was a blind spot. To see back there, the sub had to make wide slow turns to the left and right or they had to drag a towed array – sort of a remote sonar – on a cable behind the sub. Despite having rear facing torpedo tubes, the sub could not effectively use active or passive sonar for about 30 degrees astern. This, of course, was the approach of any hunter-killer subs that wanted to get a sure-fire launch at another sub target. Because of the hull nullification and the ambient noise cancellation of the SAQ system, the aft facing sensors and sonar’s now are very effective at both detection and fire control for torpedo launch. There is still some loss of resolution as compared with any other direction due to the water disturbance in the prop wash but a good sonar operator can compensate.

The final side benefit of the SAQ system is that, for the first time, it allows a sub to travel as fast as it is capable of going, even in a confined combat environment, without being detected. It was this benefit that led to the immediate cancellation of the remaining balance of the Seawolf class of subs and go directly to the Virginia class. Using a design similar to a jetski engine, called a Propulsor or jet pump, the Virginia is capable of speeds far in excess of any of its predecessors. Despite very high speeds, the Virginia class of subs will be undetectable by sonar – allowing it to move as fast as the engine can push it. Exact speeds and limits of depth of all US Navy subs is highly classified but prototype tests on the USS Jimmy Carter reached 67 knots or about 78 MPH and that was before enhancements and design changes were made. My guess is that the SSN-774 and its sister boats will be able to exceed 90 MPH when fully submerged – perhaps over 100 MPH.

The current version of the SAQ system is so effective that when it was tested in war-games against surface ships and P-3 ASW aircraft, it created a huge argument that had to be resolved by the CNO of the Navy. The USS Virginia was able to simulate the kill of all 19 ships in the exercise without being detected by any of them or by any ASW aircraft or helo. The squadron commanders of the S3 and P3 aircraft and the captains of the ASW destroyers filed formal complaints against the sub commanders for cheating during the exercise. They claimed that there was no sub anywhere in the exercise area and that the simulated kills were all as a result of cheating in the exercise computer models. The fighting between the aircraft, surface and sub communities was so fierce that the CNO had to call a major conference to calm everyone down and explain what and how the exercise went the way it did.

I am pleased that my idea from 15 years ago was eventually found to be valid and that I have contributed in some manner to our security and ability to meet any threat.

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