ASW technologies and techniques

Todjaeger

Potstirrer
I'm looking to start a discussion on the technologies and techniques used by different navies to conduct ASW. I'm looking at this from the perspective of MPA, ASW helicopter and surface vessels. What I'm interested in are the thoughts on how effective active vs. passive sonar is, and under what circumstances, also how useful things like MAD are. Also, if there are particular cases or areas where Air or Surface ASW assets are particularly useful, or useless.

For instance:
From what I understand, surface search radar is not particularly useful in locating periscopes, given current LO materials and the already small RCS and cluttered background from the ocean. Is there a method that is particularly effective in locating a periscope or sub snorkel?
 

Grand Danois

Entertainer
I'm looking to start a discussion on the technologies and techniques used by different navies to conduct ASW. I'm looking at this from the perspective of MPA, ASW helicopter and surface vessels. What I'm interested in are the thoughts on how effective active vs. passive sonar is, and under what circumstances, also how useful things like MAD are. Also, if there are particular cases or areas where Air or Surface ASW assets are particularly useful, or useless.

For instance:
From what I understand, surface search radar is not particularly useful in locating periscopes, given current LO materials and the already small RCS and cluttered background from the ocean. Is there a method that is particularly effective in locating a periscope or sub snorkel?
Right now the entire sub-affiliated community on DT is going silent (as they should).

So it is left for the rest of us to speculate...:devil

I have a question on this subject by the way. Re: surface vessels, Why can't a hullmounted sonar be used in active and passive mode at the same time (not bowmounted). Or is this some rubbish I have picked up in my cursory reading on the net?
 

contedicavour

New Member
With the growing number of SSNs and AIP SSKs, I don't think locating periscopes will be that key to ASW.
I would still bet on VDS with towed array low frequency sonars, triangulating with big ASW helos with VDS of their own. Once the hostile sub is located, the weapon of preference would be a missile containing a torpedo, such as ASROC or our MILAS system (a Teseo Mk2 SSM containing a A244S or MU90 light torpedo) that can help you engage the enemy sub 30-40km away, hopefully before the enemy sub launches a missile or a heavy torpedo at you...
Anyhow, this is Italian Navy ASW.

My question to this thread's experts is more specific : is it really useful to include your own SSK/SSNs in your ASW screen ? IMHO it slows down the surface ships (no SSK and very few SSNs can afford 30+ knots cruise speed) and it may make surface ships overcautious before launching torpedos/missiles against anything lurking underwater close to your ships !

cheers
 

Wooki

Defense Professional
Verified Defense Pro
I'm looking to start a discussion on the technologies and techniques used by different navies to conduct ASW. I'm looking at this from the perspective of MPA, ASW helicopter and surface vessels. What I'm interested in are the thoughts on how effective active vs. passive sonar is, and under what circumstances, also how useful things like MAD are. Also, if there are particular cases or areas where Air or Surface ASW assets are particularly useful, or useless.

For instance:
From what I understand, surface search radar is not particularly useful in locating periscopes, given current LO materials and the already small RCS and cluttered background from the ocean. Is there a method that is particularly effective in locating a periscope or sub snorkel?
Honestly, it depends on what wave length the radar is as to whether its useful in picking up masts from a submarine sail. In WW2 the radar of choice was the 3cm radar, as the rule of thumb is if the wave length is smaller than the target you are looking for, then you might see it.

contedicavour said:
My question to this thread's experts is more specific : is it really useful to include your own SSK/SSNs in your ASW screen ? IMHO it slows down the surface ships (no SSK and very few SSNs can afford 30+ knots cruise speed) and it may make surface ships overcautious before launching torpedos/missiles against anything lurking underwater close to your ships !
Again from WW2 the best thing to shoot down a fighter was a fighter. Its a similar philosophy with Submarines. If you want to change that philosophy, you need to create some pretty radical engagements systems.

Grand Danois said:
I have a question on this subject by the way. Re: surface vessels, Why can't a hullmounted sonar be used in active and passive mode at the same time (not bowmounted). Or is this some rubbish I have picked up in my cursory reading on the net?
Thats like going to a rock concert and setting up a sensitive microphone next to the speaker to listen for birds. Depends on the frequency of the birds mind you, but they'll be drowned out.

Why does your sonar(s) have to be hull mounted?:p4

cheers

w
 

Todjaeger

Potstirrer
  • Thread Starter Thread Starter
  • #7
I agree, the best way to counter a sub is with another sub. What I'm interested in is how effective surface and/or air assets are in ASW. A friend of mine is ex-navy and served aboard a Los Angeles class SSN. From the stories he has related, Orions and ASW helicopters aren't particularly good at detecting an attack sub. Aside from some ASW frigates with towed sonar arrays, the surface vessels really didn't know when a sub was about.

Hence my interest in the different technologies and methods used by non-subs to track/engage subs. Again, from what was related to me, the MAD designs in use in the early to mid-90s weren't sensitive enough, at least to detech US subs. From a post in DID from last year, Australia is working on a new MAD device that is more sensitive. Another thing is that the US Navy is now switching to searching for enemy subs using active, instead of passive sonar.

From what I understand, the ASW equipment on board is as follows:

For helicopters:
dipping sonar
air-drop torpedoes and/or depth charges

For MPA:
sonobuoys
MAD
air-dropped torpedoes

For ASW vessels:
hull and towed sonar
torpedoes
A/S mortars
depth charges
ASW rockets
ASROC or other rocket assisted ranged torpedoe system

Is there work being done on developing alternate methods for sub detection?
While much has been done to reduce the acoustic signature of a sub, can a sub be tracker thermally? As had been mentioned in a prior thread, subs leave a wake, at least in shallow water. Can a vessel or aircraft detect and track such a wake, or is it too small to detect without the area perspective given by satellites?:unknown

I'd like to hear people's thoughts on this, at least the ones they are free to share.

-cheers
 

Sea Toby

New Member
While I won't touch ASW, I do have a comment to make about the speed of aircraft carriers. Nimitz class aircraft carriers are capable of more speed than the listed 30+ knots. One of my brothers was on the Nimitz during the Iranian hostage crisis, when the Nimitz sailed around Africa to reach the Arabian Sea off the Persian Gulf. The Nimitz left her conventional fueled escorts behind, the only warships able to keep up with her were her nuclear powered cruisers escorts. The Nimitz consumed so much of her nuclear fuel that afterwards she had to be slowed down somewhat by Admiral Rickover to reach her next scheduled refueling. Yes, there is only one shipyard which can do this, and it can only do one aircraft carrier refueling at a time.

Usually in transit a nuclear powered aircraft carrier runs around 20 or so knots, only in aircraft operations does it speed up to 30 knots. So yes, a nuclear powered submarine capable of speeds above 20 knots can keep up with a aircraft carrier battle group along with the rest of the escorts and replenishment groups.

As I have attempted to say before on another thread, the faster a ship goes the less range it receives. Every ships sail at their economical fuel consumption speed, even though they are capable of faster speed. Even nuclear powered aircraft carriers have limits, they do have to reach their next scheduled refueling in a few years. Considering a nuclear refueling takes a year or more, and with the US Navy having several nuclear powered aircraft carriers, their scheduled next refueling is booked years in advance.

It won't be long before the US Navy has nothing but nuclear powered aircraft carriers. Since one of the US Navy's nuclear powered aircraft carriers will be undergoing refueling, the Navy dropped one of its carrier airwings. While there maybe 11 nuclear carriers in the fleet, only 10 will be operational, there is no need for an 11th airwing.
 
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Grand Danois

Entertainer
Thats like going to a rock concert and setting up a sensitive microphone next to the speaker to listen for birds. Depends on the frequency of the birds mind you, but they'll be drowned out.

Why does your sonar(s) have to be hull mounted?:p4

cheers

w
I know towed arrays should be better for subhunting. I was curious about the bow-mounted vs hull-mounted configuration. But I led myself astray.

I was wondering why a particular class of Indian destroyers didn't have a bow-mounted sonar, and investigated hull- vs bow-mounted config. Then I had a look at the particular sonar and didn't realize it was performing the functions of a bow-mounted sonar and not the high-powered lowfrequency typical of ASW hull-mounted.

In hindsight I should have caught this. ;)

Question on ASW surface vessels. If subs are the superior ASW weapon, why bother with ASW frigates/vessels at all?

Why not focus on SSN/SSK and in the future UUV and static sensors, perhaps launched from general purpose surface vessels? (BAMS)
 

Todjaeger

Potstirrer
  • Thread Starter Thread Starter
  • #10
Question on ASW surface vessels. If subs are the superior ASW weapon, why bother with ASW frigates/vessels at all?

Why not focus on SSN/SSK and in the future UUV and static sensors, perhaps launched from general purpose surface vessels? (BAMS)
Indeed, that was part of why I started the thread. As mentioned above from a former sub crewmen, ASW assets like helicopters and Orions as of little use against current subs (at least modern Western attack subs). If these assets are not of much use, why is the US developing the p-8 MMA? If it is to be a MPA with patrol and ASV capacity, that makes sense. But still having an ASW capacity? Or are the aircraft of greater use then my friend seemed to indicate?

-Cheers
 

Wooki

Defense Professional
Verified Defense Pro
I know towed arrays should be better for subhunting. I was curious about the bow-mounted vs hull-mounted configuration. But I led myself astray.

I was wondering why a particular class of Indian destroyers didn't have a bow-mounted sonar, and investigated hull- vs bow-mounted config. Then I had a look at the particular sonar and didn't realize it was performing the functions of a bow-mounted sonar and not the high-powered lowfrequency typical of ASW hull-mounted.

In hindsight I should have caught this. ;)

Question on ASW surface vessels. If subs are the superior ASW weapon, why bother with ASW frigates/vessels at all?

Why not focus on SSN/SSK and in the future UUV and static sensors, perhaps launched from general purpose surface vessels? (BAMS)
$$$$ Ka ching $$$$$ The idea is to make commies go broke, not the USA. A frigate is a lot cheaper then a sub...

A UUV operating from a surface ship is a lot cheaper then a UUV operating from a submarine too. Its all about energy management and launching/recovery from the surface allows you to do more things that would be difficult to do from a submarine. For example you could launch more as (depending on your UUV tech) you might be placing a strain on the submarines systems. Simple things like processor cooling come to mind.

cheers


W
 

Ozzy Blizzard

New Member
hang on so how usefull are ASW surface platforms then? I was under the impression that a desent frigate with a towed aray, and a helo with a dipping sonar would be a real pain in the ass for an SSK/SSN. How hard is it for a sub to detect a decent frigate say a modernized OHP doing sprints, out at the 2nd and 3rd CZ's? Sure the subs got an advantage because its got the thermocline to hide behind but its got to deal with several platforms simultaniously, wouldn't an intgrated surface defence have the advantage? Also why would the yanks switch from passive to active for hunting subs? I thought that was the ruskies bit, cus their passive stuff wasn't too crash hot, and you dont know if you've been detected with passive, rather than just setting up a wall of sound for the bad guy to penitrate, so why would the USN go down the apparantly simple path??? :unknown
 

Salty Dog

Defense Professional
Verified Defense Pro
Right now the entire sub-affiliated community on DT is going silent (as they should).

So it is left for the rest of us to speculate...:devil

I have a question on this subject by the way. Re: surface vessels, Why can't a hullmounted sonar be used in active and passive mode at the same time (not bowmounted). Or is this some rubbish I have picked up in my cursory reading on the net?
You might have come across material on the AN/SQS-23 PAIR which were (2) hull mounted sonar domes found on the USN DDG-2 (Chales F. Adams) class. I recall the front dome was active/passive whilst the rear dome passive only.
 
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Salty Dog

Defense Professional
Verified Defense Pro
hang on so how usefull are ASW surface platforms then? I was under the impression that a desent frigate with a towed aray, and a helo with a dipping sonar would be a real pain in the ass for an SSK/SSN. How hard is it for a sub to detect a decent frigate say a modernized OHP doing sprints, out at the 2nd and 3rd CZ's? Sure the subs got an advantage because its got the thermocline to hide behind but its got to deal with several platforms simultaniously, wouldn't an intgrated surface defence have the advantage? Also why would the yanks switch from passive to active for hunting subs? I thought that was the ruskies bit, cus their passive stuff wasn't too crash hot, and you dont know if you've been detected with passive, rather than just setting up a wall of sound for the bad guy to penitrate, so why would the USN go down the apparantly simple path??? :unknown
I feel the submarine will always have an advantage over ships as they are the experts in the acoustic environment, they are quieter, and they can move in and out of the various acoustic layers to their advantage.

I will say that ship/air ASW will have an advantage especially with an integrated effort (I know the bubbleheads will disagree). In any case, if the surface effort keeps the sub away and prevents an attack, they have done their job.

The active sonar hunting/attack I feel is a carry-over from the WW II days when ships went barreling towards the submarine target to track and attack. In the 80's, ASW training for ships (especially with bow mounter sonars) continued to advocate this tactic and it was practiced routinely at sea and in trainers. This frequently involved a pair of ships taking turns tracking and firing ASW weapons. Rotary/fixed wing assets are used if available. Mind you, this was training and it was always felt that in a real war scenario the tactic would be to distance yourself from the underwater contact and send in air assets for tracking and the kill.

US warships strive to be quiet a sea taking care to have machinery on acoustic isolation mounts. This is a reason why USN warship propulsion stubbornly maintains COGAG propulsion vice more fuel efficient CODAG/CODOG systems. USN warships also have the PRAIRIE/MASKER system to further reduce their noise signature.
 

submerged

New Member
no matter how good the dampening and insolation is, the screw will allways give away a surface vessel at more then silent speed ahead, this is one of the main reasons for airborne ASW units combined with their greater speed wich can be used to triangulate a submerged target.
 

Systems Adict

The Bunker Group
Verified Defense Pro
Thats like going to a rock concert and setting up a sensitive microphone next to the speaker to listen for birds. Depends on the frequency of the birds mind you, but they'll be drowned out.

Why does your sonar(s) have to be hull mounted?:p4

cheers

w
As brushed over by others in the thread, there are reasons why the sonar dome is bow mounted.

#1. Provides the greatest possible distance AWAY from the noisy parts of the ship (stabilizers, engines, M/C spaces & props), meaning that there's less things to interfere with the incoming signal.

#2. Towing a sonar array adds a certain amount of danger to the ship conducting the process. Control of depth of the array, distance from ship, the ships course & speed, make up of the layers of the water, any threat / perceived threats from subs, fishing nets, etc.
All these added to the additional factors of towing a large object on the end of maybe 2 to 4 kilometres of cable which must send & receive signals while being buffeted by 15 - 25 knots of flow, puts a lot of stress on the components, implying that failures are quiet common.

#3. The shape of the dome cover actually helps the ship break thru the water (bulbous bow), producing less noise & reducing friction, allowing the ship to move a little faster in comparison to a standard V-form hull.

Your comments / remarks are appreciated...


System Adict
 
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Salty Dog

Defense Professional
Verified Defense Pro
As brushed over by others in the thread, there are reasons why the sonar dome is bow mounted.

#1. Provides the greatest possible distance AWAY from the noisy parts of the ship (stabilizers, engines, M/C spaces & props), meaning that there's less things to interfere with the incoming signal.

#2. Towing a sonar array adds a certain amount of danger to the ship conducting the process. Control of depth of the array, distance from ship, the ships course & speed, make up of the layers of the water, any threat / perceived threats from subs, fishing nets, etc.
All these added to the additional factors of towing a large object on the end of maybe 2 to 4 kilometres of cable which must send & receive signals while being buffeted by 15 - 25 knots of flow, puts a lot of stress on the components, implying that failures are quiet common.

#3. The shape of the dome cover actually helps the ship break thru the water (bulbous bow), producing less noise & reducing friction, allowing the ship to move a little faster in comparison to a standard V-form hull.

Your comments / remarks are appreciated...


System Adict

My experience is limited to the USN/Brazilian sonars so here's some items to complement:

1) I only know of low frequency (2.6-3.5 kHz) sonars such as the AN/SQS-26/53 (FF-1074, DD-963, DDG-993, DDG-51, CG-47) which are bow mounted due to the the size of their transducer array. The bottom of the sonar dome adds some 3 meters to the draft below the keel. Had this been hull mounted, it would have added even more to the ship's navigational draft.

Hull mounted sonars are typically medium frequency (6.8-8.2 kHz) and smaller such as the AN/SQS-56 (FFG-7) and EDO 997(F) (Niteroi class Frigates-Vosper Mk-10) so are hull mounted at the keel.

Sonar frequency factors into the size of the transducer array which results in final location, bow or hull (keel) mounted.

2) I was not aware of any active towed arrays of the TACTAS type. The AN/SQR-19 is passive and stand alone. The older AN/SQR-18 was also passive but was towed by the AN/SQS-35(V) IVDS the latter was a medium frequency active/passive sonar. The AN/SQR-18/19 are both passive low frequency.

Also note that SSNs use passive towed arrays and are subject to tow conditions previously mentioned.

3) Whilst the bow mounted sonar dome added a certain degree of motion stability and hydrodynamic efficiency as cited above, it was not without concerns from the seamanship point of view.

As the dome itself is a physical protrusion at the bow, great care has to be taken in alongside maneuvering when docking/undocking the ship. Even the correct positioning of tugboats at the bow was essential.

Not to mention keeping an eye on the anchor chain should it be caused to rub against the sonar dome.

The AN/SQS-26/53 sonars have rubber windows (SDRW - sonar dome rubber window) on the front and sides, and the dome itself is pressurized with fresh water. Rough sea conditions warranted a close watch on the sonar dome pressure especially when the bow dome would be pulled out of the water then come slamming down. Sometimes this would limit the ship's transit speed just to take care of the dome.

The SDRW could tear, and if so, warranted an immediate full drydocking and replacement of the SDRW. I experienced a 6-inch tear in a SDRW and we limped back to port at 8 kts for drydocking.
 
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Salty Dog

Defense Professional
Verified Defense Pro
Fish Hawk

Raytheon Proves Advanced Anti-Submarine Capability with Successful Flight Test

Fish Hawk weapon system accurately flies more than 10 nautical miles to
preplanned target


EGLIN AIR FORCE BASE, Fla., May 14, 2008 /PRNewswire/ -- Raytheon
Company (NYSE: RTN) has entered the U.S. Navy's High Altitude
Anti-Submarine Warfare Weapons Concept (HAAWC) competition, successfully
demonstrating a new weapon system -- the Fish Hawk -- March 21 at the Eglin
flight demonstration range in the Gulf of Mexico.

The Fish Hawk is a kit that attaches to Raytheon's MK54 lightweight
torpedo and enables submarine-hunting aircraft like the P-8 Multi Mission
Maritime Aircraft and P-3 Orion to precisely deploy torpedoes from high
altitudes while standing off a safe distance from a target.

During the March demonstration, an aircraft flying at 15,000 feet
jettisoned a Fish Hawk-equipped dummy torpedo. The Fish Hawk's wings
rapidly deployed and the weapon system then glided more than 10 nautical
miles, splashing down well within the small target area and achieving all
primary test objectives.

"This flight test successfully demonstrated the ability of Fish Hawk to
accurately place the MK54 torpedo on target after release from a
high-altitude aircraft like the P-3 or P-8," said Ken Pedersen, Raytheon
vice president of Advanced Programs. "We look forward to leveraging our
expertise as the world's leader in precision guided munitions and
presenting the customer with a cost-effective design that meets or exceeds
all HAAWC requirements."

The kit is composed of wings that deploy after the system is released
from an aircraft, a control section and a Global Positioning
System-Inertial Navigation System precision guidance system. The kit is
designed to enable both the P-3 and P-8 to maximize loadout by deploying
the system from the aircraft bomb bay.

Fish Hawk offers new capabilities that will enable aircraft to launch
from higher altitudes and thus enhance survivability. The system also
provides longer time on station thanks to reduced fuel consumption.
Additionally, Fish Hawk reduces airframe stress because the aircraft is no
longer required to dive down to the target in order to deploy an
anti-submarine torpedo.

Raytheon Company, with 2007 sales of $21.3 billion, is a technology
leader specializing in defense, homeland security and other government
markets throughout the world. With a history of innovation spanning 86
years, Raytheon provides state-of-the-art electronics, mission systems
integration and other capabilities in the areas of sensing; effects; and
command, control, communications and intelligence systems, as well as a
broad range of mission support services. With headquarters in Waltham,
Mass., Raytheon employs 72,000 people worldwide.

Note to Editors:

Co-developed by Raytheon and the U.S. Navy, the MK54 is a
next-generation anti-submarine warfare weapon that is deployed from a
surface ship, helicopter or fixed wing aircraft to track, classify, and
attack underwater targets. Sophisticated processing algorithms allow the
MK54 to analyze the information, edit out false targets and
countermeasures, and pursue identified threats. The MK54 is designed for
both deep water and littoral environments, making it the only lightweight
torpedo capable of striking any target in the world's oceans, regardless of
water depth.
New long range air dropped ASW weapon for the P-3 and P-8.
 

Salty Dog

Defense Professional
Verified Defense Pro
With the Fish Hawk system, P-8 and Mk-54, airborne ASW takes a leap forward, or does it?

The P-8 will replace the venerable and reliable P-3 in the USN.

The S-3 retires this year with no fleet replacement. This clips the long range airborne ASW once enjoyed by the CVBG.

What about European and Russian airborne ASW systems?

How about next generation airborne ASW systems? Any significant developments in this area, or just current sensors with better processing capabilities?

Worth a discussion in view of the current and next generations of SSNs and SSKs.
 
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