More ASW Goodness

So let’s talk for a minute about the environment that ASW takes place in: The Ocean.

Unlike combat on land, or even on the water’s surface,  hunting the enemy underwater has a unique set of variables that must be taken into consideration. For starters, you can’t see the target, and he can’t see you. It’s the one element where, for all intents and purposes, both sides are fighting blind. That doesn’t mean we can’t “see” the enemy, but it means we can’t visually ID him. We have to use our sense of hearing as our prime sensor.

Now the Ocean is made up of salt water, and has an enormous number of life forms which call it home.  These, too, must be taken into consideration, because they make sounds which will interfere with our target’s sounds. Additionally, there are all sorts of vessels plying their trade up on the surface, and they also radiate noise into the water, which will bounce around and help mask our elusive prey.  So what to do, what to do.

As talked about in other posts and comments, you can plop a hydrophone into the water and listen. You can get general information that way, but to get the information in a manner that alolows us to locate, fix, and attack or track a target means we need to refine the data.

Sound in water is affected by a variety of environmental variables. The three general effects are Absorption, Refraction, and reflection.  These will muffle, scatter, or bounce the sound waves as they travel between the noise maker and the listener.  To these three general effects must be added some physical ones: Temperature, Salinity, and Pressure, known as the “TeaSPoon” effects.  The lower the temperature, the faster the sound waves will travel, because the molecules which vibrate are closer together, and therefore use less energy transmitting the sound, thus allowing for more energy to be transmitted. Salinity and pressure also add speed, due to making the water more dense.  Considering the speed of sound 4388 feet per second, the equation is thus:

4388 + (11.25 × temperature (in °F)) + (0.0182 × depth (in feet)) + salinity (in parts-per-thousand )

This will give you a close approximation of the actual speed of sound and can be further refined if needs be.

Now, sound is also effected by pressure in two ways: The more deep the sound goes, the more resistance it meets until eventually it is bent upwards. It will then travel upwards until it reaches the thermocline, where the warmer water will bend the sound back down and the process will repeat. The stronger the sound energy, the longer this pattern can repeat.  I have personally tracked one intense sound source, traveling in this manner,  more than 400 miles away.  The name for this effect is called a “convergence zone”.  If you could look at it visually, it would appear as a series of ever-expanding donuts. Inside of each donut, the sound will appear to the listener as a “direct path”, but once you reach the donut hole, or get outside the donut, the sound drops off.

When a Convergence Zone, or “CZ” as it’s called in the trade, is not present, then almost always you will have “direct path” contact. that means that the sound radiating from the target is traveling directly to the hydrophone with little to no interference.

More data here

How do we deal with all of this data? How does this come into play? Here follows a general overview for a crew operating a P-3 Orion.

On the way to the station, the crew is developing the basic environmental data. The Op Area has already been defined for them, developed from other data and presented at the briefing. The distance to the Op Area will determine the amount of time spent on station. Missions usually lasted 10-12 hours, and the shorter the transit time, the better.

Once onstation, the crew will drop a BT buoy to garner local temperature data and add that into their equations.  The environmental data (coupled with the type of target) will determine what distance to space the sonobuoys, and also what type of pattern (and how many buoys) they will be dropped in.  The P-3 can monitor 16 buoys at one time, and has a maximum of 31 separate channels to receive the data on.  Technically, you could drop 31 buoys, and monitor them alternately, but that is never done.  You use one pattern to generate contact, then add more buoys to refine the data as the situation develops.

The normal pattern is a single line, called a barrier, across the estimated path of the target.  These barriers can be many miles long, with the buoy spacing designed so that their detection ranges overlap, not leaving any dead zones for the target to slip through. It’s just like having overlapping fields of fire for machine guns, artillery, or even radars.

One other modifier should be talked about: weather. Weather affects both the target and the crew on the P-3. It isn’t a whole lot of fun bouncing around in turbulence for hours at a time, and the crew’s effectiveness can easily be degraded. If the storm is large enough to increase the sea state and wave height, then it can (and will) rip the hydrophone cables right out of the buoy. Rain will also cause  more noise on the surface, which, for the most part only effects shallow water, or littoral areas, and targets operating in the thermocline.

In the old days, Soviet subs kept a careful eye on the weather, and would maneuver whenever possible to be under the local thunderstorm. It used to be a standing joke amongst the flight crews that the easiet way to find a sub was to locate the nearest storm cell in the op area.

Okay, that’s the basics. next post will talk about tactics, and what happens onstation.

P-3 Orion in Old School Colors


11 Responses to “More ASW Goodness”

  1. 1 Jason
    March 27, 2010 at 20:57

    Just wanted to say thank you for posting these. They’ve been very interesting.

  2. 3 SCOTT the BADGER
    March 27, 2010 at 21:34

    As an Orion is an all weather plane, what is your patrol altitude in rough weather? You must be up there a bit, so as to avaoid sudden downdrafts ruining your day.

  3. March 27, 2010 at 23:18

    Normally, we try to cruise above 10,000 feet. At altitude, you can also conserve fuel by shutting down one of the outboard engines. Sometimes it was impossible to climb above the stuff and you just had to batten everything down and deal with it.

    When the crew are rigging ships, or going down mad-trapping, then we’re about 300-500 feet

  4. 5 steve
    March 27, 2010 at 23:49

    I was a Track Sup on a CGN in the Med in 76. It was always a good thing to have a P-3 out and about. I think everyone took ASW a lot more seriously back then.

  5. 7 clarkward
    March 28, 2010 at 11:05

    From my experience playing bad guy on an SSN against our carrier groups, ASW is sadly lacking in our surface fleet. Really the only thing that stood a good chance of netting us was air, either P-3 (not often in CVBG war games) or a helo. We had a really fun time against the Teddy Roosevelt where we drove under a line of DDGs pinging away (we were maybe 150/200 feet down) without detection, and came to PD for some beautiful pics. Got several of the carrier on my wall right now, and the CO got a nice one of the DDG captained by his ‘napolis roommate. I suspect he really enjoyed that one. But back to ASW, apparently all the noise from the yobbos being active masked our own noise!

    The way we did ASW when I was in (94-2003) was not very good. Nuke boats were used with limitations on ops to simulate SSKs. Not bad, since we lacked SSKs to use. BUT, safety measures were used by the hunters as targeting aids, reducing the amount of skill necessary to conduct ASW ops. I speak of the ‘stovepipes’, circular no-go areas for the surface ships which were present for submarines to safely come to PD or surface in extremis without collisions. The DDGs would troll just outside these areas (which were on their charts for obvious reasons), knowing we had to use one of them and that we had to transmit every so often. We (as a target) had to run our diesel every 8 hours and had other strange requirements put on us (put up more masts than usual to present a bigger radar target, for example).

    My suggestion is to task SSNs on short underways (2-weeks to a month) with a couple of training sessions for DDGs; let them hunt for a few hours at a time, come to PD and exchange feedback, go for another round. One on one, or even 2 DDGs in a training evolution with 1 SSN, without the pressure on the CO of ‘my ship must win win win’ that would be present in a graded wargame. On one underway, we obliged the CO of a DDG by conduction various operations on a known course so his sonar crew could train up on what these evolutions sounded like and run tracking drills that he could evaluate (since he knew our course, turns made, etc).

    The USN needs to get it’s ASW game up, big time. If Admiral Harvey is reading, I’d be happy to help for the low low price of an EM1(SS)’s salary(over 8), with sea pay, sub pay, nuclear supervisory pro pay, etc, and all the coffee I can drink. 8)

    • March 28, 2010 at 14:49

      Oh, you’ve got not complaints from me regarding the lack of ASW training. I am in full agreement with you. The problem with training against our own nuke boats is that, as you say, they have to add noisemakers to aid in detection. Even then, we’re going against our own boats, and NOT those of the nations we might potentially face.

      This past year or so, there was a (I believ) Dutch SSK on the West Coast for a number of months, playing games (intentionally) with out surface fleet and MPA assets. That was good, because it could play itself, and was commanded by an officer and crew who WERE SSK drivers.

      The big difference, to my mind, is that if we face a nation like China, the PLAN will not be using single SSK’s, but wolfpacks, and we’ll be having to deal with multiple threats.

      It all comes down to training. I know that, in my days (76-84) we had constant training in the simulator(s), as well as in real life.

      I have serious concerns about our effectiveness these days, because I expect us to be tested in the near future.


  6. 10 Flugelman
    March 28, 2010 at 21:35

    As an old P-3B RO & IFT I am enjoying your ASW series. Brings back too many memories. On the subject of ASW training against our own boats, I seem to remember that once they got tired of playing they could just disappear. “Poof”…

    My first visit, nice BLOG. Stay safe.

    • March 28, 2010 at 22:06

      Thanks for the kind words! The RO’s & IFT’s were important to the crew in our old “analog” days!

      And yeah, it always seemed like anytime we started to get the upper hand on one of our own boats, they’d just shut off the noise and float away. The old joke was that the easiest way to track one of our boomers was to listen for the sound of silence. 🙂

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