If the Coast Guard should ever again decide it needs a submarine detection capability, there may be a way to add it to vessels as small as the 87 ft WPBs.
The Navy is currently fielding a new version of it’s ASW helicopter, the MH-60R, and it’s new dipping sonar is proving much more effective than it’s predecessor. The complete sonar system can weigh less than 600 pounds.
The Soviets also used dipping sonars, but not just on helicopters. They used them on small surface craft as well. These vessels would work in teams using a sprint and drift tactic.
The same transducer might also be hull mounted with relatively little impact. There is also the possibility that with relatively minor modifications it could be made into a towed variable depth sonar. A combination of hull mounted transducer and variable depth sonar working off the same console could offer some advantages.
Certainly not very effective for chasing nucs, and I’m not suggesting we need a big program to look for Narco subs, but, should the need arise, it could be work against the ultra quiet but slow moving diesel electric subs that might lurk in the high noise areas of the littorals.
Chuck Hill's CG Blog 
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Sounds like a plan. Let’s do it. If the Coast Guard is still an armed sea going military service, and it is, it needs to re-aquire some basic sub detection capability. Especially with the new threat of narc subs. Sounds like a good idea.
Too large for an 87′-footer but gives the general idea.
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I remember VDS from the mid-1960s. Just the notice that VDS was being streamed would send Soviet subs scattering; not of detection but because of possible ramming. The Soviet subs used to shadow the fleets.
The largest change would not be in equipment but culture. Is the Coast Guard ready–yet again–to take on such a role? What is being done to alter the current outlook in the future officer corps?
Bill, I think you would agree that we were never really ready in the past, so I’ll be flippant and say why should this time be any diffferent?
We have been lucky to have had many years of relative peace and maritime dominance by the US. The Officer corp is remarkably adaptable. Before it becomes a crisis, the service will see it coming and attempt to adapt. Problem is, we have relatively little expertise and the institutional mechanisms are not in place to make good decisions about integrating CG assets into the larger defense planning systems. The NSCs seem to have been an opportunity lost, in that for a relatively small increase in cost they could have been credible warships.
Yes, there is liaison and the planning documents, and the Navy does buy us some equipment, but there is no provision for the Navy saying, “If the Coast Guard builds their ships with these capabilities, then the Navy will not have to build that type of ship and because it will result in a net savings to the country, the Navy budget will pay the incremental cost of making a more capable cutter (or airplane).”
So, once it is detected what do they do? No ASW weapons…..
This is only “relatively painless.” When you start moving things around it has a domino effect. But if we wanted them, there are weapons out there. Even small vessels can carry ASW torpedoes. They are much smaller than the torpedoes that were carried by WWII torpedo (PT) boats that were wooden boats only 78 to 80 feet long that normally carried four torpedoes. Even so there might be stability concerns that would require moving or beaching some of the existing outfit.
World War II: Length: 24 ft (7.32 m), Weight: 2,840 lb (1288 kg), Diameter: 21 in (53 cm)
Modern ASW torpedo: Length: 8 ft 6 in (2.59 m), Weight: 508 lb (231 kg), Diameter: 12.75 in (324 mm)
WWII: http://en.wikipedia.org/wiki/Mark_15_torpedo
Modern: http://en.wikipedia.org/wiki/Mark_46_torpedo
I’m familiar with ASW torpedos. We used to have them on our ships. Mk 44’s when we first got them, I think they moved to the Mk 46 later. I went through the Navy Torpedo school in San Diego with an FT so we would learn about them.
Historically the CG has been deeply involved in ASW with a history going back to WWI, peaking in WWII. When I entered the CG we still had 36 ASW capable ships and the 378s were starting to come out. 378s weren’t great ASW ships but they were as capable as many of the active Navy destroyer escorts of the time.
There are light weight torpedoes newer than the Mk46, the Mk 50 and 54, but they are essentially the same size. On the other hand, its hard to realize how big the heavy weight torpedoes were and are, they were truly big brutes. Re the PTs apparently they were originally equipped with the similar but older Mk 8 and as the war progressed they were rearmed with the air launched Mk 13 that did not require tubes. They were a bit smaller than the standard surface vessel torpedoes, but at over 2,200 pounds, still about four times the size of the ASW torpedoes.
I suspect that if we were only after the drug running subs, their diving depth would not be great and we could probably bring them up with concussion grenades.
“…Certainly not very effective for chasing nucs, and I’m not suggesting we need a big program to look for Narco subs…”
Ship-mounted sonar and subs are very ineffective against narco smugglers (i.e., SPSS) – see CDR Pfeiff’s work on SPSS Detection. His op analysis is now part of doctrine for SOUTHCOM and the CIT Task Forces. The real solution is more MPAs and better analysis of departure and destination points.
Click to access 09Jun_Pfeiff.pdf
http://www.nps.edu/About/News/NPS-OR-Team-Optimizes-Defense-Against-Narco-Semi-Subs-.html
The reason the torpedos used agaisnt surface ships were so big is that it required a lot more high explosive to sink a ship on the surface. For a sub smaller torpedos work fine because all you need is to punch a hole in the pressure hull.
CDR Pfeiff’s study was about detecting semi-submersibles. It presumed there would be a platform available to make the actual intercept, and to intercept semi-submersibles you don’t need sonar, since they are just low lying surface vessels. The MPA he talked about (including CG c-130s) were using radar, not sonar, for detection.
If we are going after true narco-subs MPA (P-3s and P-8s) are certainly the best way to search a wide area, and if ROE permitted destruction upon detection, they would not need any help. But if we can’t do that (shoot first, no questions asked), we will need surface vessels to take the hand off from the aircraft, develop a target solution, force the sub to the surface, and seize the crew.
Surface ships searching for subs that don’t want to be found on the open ocean has never worked very well, but surface vessels are also potentially useful for initial detection when forming a continuous barrier where geography limits the subs options, as at the departure and destination points or at focal points like straits (or protecting targets like convoys, but not relevant for narco-subs).
As I said, “I’m not suggesting we need a big program to look for Narco subs.” We don’t know if this is really a serious threat or just a one-off experiment. I have serious doubts as to the narco-sub’s viability.
Since the torpedoes now explode under the ship instead of against the side, torpedoes are much more effective against surface vessels than they used to be, so for the same size ship you could use a smaller warhead, but generally ships have gotten much bigger since WWII, so subs still need the big warhead.