ASW and defended corridors

The few dozen ASW (anti-submarine warfare) destroyers and frigates in European navies are not going to suffice to protect European overseas shipping against a blockade or disruption campaign that uses many submarines. The U.S.Navy has more ASW warships (and SSNs), but any claims that it could defend American maritime trade against a fleet of SSIs (conventional submarines with air-independent propulsion) is laughable. They are worse prepared for that job than in 1941.
The ratio of escorts to cargo ships, ports and routes is simply too bad. Many if not most ASW ships would furthermore be needed as escorts in naval actions (same as the USN's problem in 1942) and many if not most would likely be revealed as ineffective once put to the test of a real war.
ASW aircraft, the handful of SSNs and the handful of (slow) SSIs aren't going to change the general picture of insufficient resources IF there was a major challenge by undersea forces.

I wrote back in 2009 about the (in my opinion actual) European naval power needs, and concluded that an offensive strategy to securing maritime trade would be successful and wise economically. I stick to this opinion, but it's interesting to think about what would at least be feasible (affordable) as a defensive and effective European (ASW) effort.

Well, the ratios are undeniably bad, so one needs to work on those. A reduction of routes would help greatly, and a reduced emphasis on the expensive and slowly built ASW warships. Navies L_O_V_E ASW frigates et cetera because navies are focused on hulls, on officer career opportunities, on prestigious things to show off*. They are by their nature not much interested in what air forces can contribute to ASW, in fixed installations, in land-based assets, in mines et cetera. There were interesting American efforts during the Cold War such as SOSUS and CAPTOR, but I'd like to assert that particularly the European navies have become even more focused on their pet interests (hulls, officer slots, prestigious things...) than before they suffered from the "peace dividend".

Naturally, that's where room for improvement should be searched first: All that stuff that navies don't like all that much, maybe even fear instinctively.

So, how about this?

Defended corridors could be established** with***
(1) anchored floating radar decoys
(2) area surveillance sonars (multistatic very low frequency active sonars, both operated by tug ships and semi-stationary like SOSUS)
(3) land-based ASW helicopters with dipping sonar and lightweight torpedoes that verify possible contacts and if need be engage them
(4) land-based anti-submarine missiles (~ASW-SOW "Sea Lance", with in-flight impact point update), on call by the ASW helicopters and possibly used to deploy lightweight torpedoes in patterns to prevent the sub's escape by sprint
(5) mine countermeasures assets that create and recreate/maintain safe lanes close to harbours
(6) unmanned submersible inspection drones that verify possible contacts even if helicopters 
(7) acoustic decoys employed by boats (to make over-the-horizon attacks with sub-launched missiles too inefficient)

I don't even suggest to use frigates for this because their sonar wouldn't offer anything on top of this and the same applies to their onboard helicopters.

The civilian ships moving through these corridors would at the very least possess a towed radar and sonar decoy, and torpedo fuze-triggering decoys against wakehoming torpedoes. They would also deploy chaff and multispectral clouds if they spot incoming missiles or get alerted at such a threat by radio.

Such defended corridors could be established as follows:

Rotterdam-London (Royal Netherlands Navy)
London-Le Havre (Royal Navy)
Le Havre-Bordeaux (French Marine Nationale)
Bordeaux-Lissabon (Armada Española)
Lissabon-Gibraltar (Marinha Portuguesa)

This would be akin to the different sectors defended by the different national contingents in Central Europe during the Cold War (both in regard to land forces and area air defences). 
I'm not proposing a German-run corridor because a Hamburg-Rotterdam corridor would be rather long and expensive compared to the modest role of German North Sea ports compared to the huge port at Rotterdam (Hamburg has only about 1/3 the cargo throughput of Rotterdam) and Germany needs to provide more pressing defence efforts than ASW due to its relative vicinity to the Eastern NATO and EU frontier.

The Mediterranean could be sealed off at the Bosporus (Türk Deniz Kuvvetleri/Turkish naval forces effort) and at Gibraltar (Royal Navy and/or Armada Española effort), with the same or similar technologies as used in the defended corridors.
SSIs and SSNs could track their unfriendly counterparts in peacetime or times of crisis, ready to pounce once war breaks out.
_ _ _ _ _

Navies are not interested in much of this, of course. They want ships, officer career opportunities, prestigious objects etc. The current Western naval strategies are reliant on land-based offensive efforts against bases (good choice), tracking, maritime surveillance, some mine countermeasures and otherwise the Western navies are all about "interventions": Things such as a battalion of marines or two to be landed in some Third World country, some disaster relief, some naval blockades for embargo enforcement, some launching of ship/land cruise missiles and naval aviation. There's no real concept to secure maritime trade directly, unless one has a ridiculous amount of confidence in the (implausible) ability to seal off the GIUK gap.



*: Just look at how often they talk and write about "showing the flag", a usually perfectly benefit-free exercise.
**: Effective width (unless restrained by land masses) equal to 2.5 times the realistic fibre-optic torpedo guidance range.
***: Protection against armed merchantmen would additionally require a surveillance, tracking, identification and boarding capability. This could be done with over-the-horizon radar (surveillance, tracking) and helicopters (ID and boarding) or alternatively many fishing boats with a few marines onboard each substituting for the helicopters.

P.S.: I know that this is mostly a clarification of what I wrote in September 2015. The assignment of corridors to the countries is an in my opinion intriguing addition, though.


  1. Just about your 7 points:

    1) I don't understand why are necessary floating radar decoys.
    2) Very low frequency sonar turns me (and Greenpeace) mad. For me is like, in land, to burn forests In order to deny places to hide for the enemy. I can understand to activate them in a located place for some minutes, but by default: they should be passive sonars.
    3) ASW helicopters are good, but they should not be alone. I think that a faster response (and at increased range) is also desirable. I am referring to good MPAs (Atlantique, P-3 Orion,...) with a big enough load of different types of sonobuoys and light torpedoes to investigate a contact for long, long time (and engage it). One problem in Europe for ASW is that we have an aging fleet of MPA... without substitute (P-8 is not cheap enough).
    4-5) Ok.
    6-7) I think that those UUV (Underwater Unmanned Vessel) for inspections (and to act as acoustic decoys) should be torpedo-like, but "recoverables". If they are like torpedoes then they can be launched by ships, aircrafts, subs... and even by rockets without needing new adaptations. I think that the recovery part is the tricky one: You can use for that mission a big manned ship (ASW frigate or OPV)... or perhaps an USV -Unmmanned Surface Vessel- or UUV -Underwater- (far bigger than a torpedo but far smaller than a manned ship) ... and then open the possibility that those middle-size Unmanned Vessels could have a mini-helipad for mini-helicopters ;-)

    1. 1) Effective torpedo range is very limited compared to submarines' ability to launch missiles at surface ships. Lots of radar decoys would make this much less effective, even if the missiles recognize the decoy as such (which won't happen until the missile is quite close and thus wasted much fuel with a pointless approach).

      2) Passive sonars are close to useless nowadays against conventional submarines with AIP such as Typ 214. The first detection would likely be in almost all cases by LFASS.

      3) ASW aircraft cannot use dipping sonars.

      UUV) What matters is that the false contacts get sorted out quickly. ASW missiles are expensive.

    2. 1) ASM (Anti Ship Missiles) usually start seeking mode once they are in their programmed zone to start attack, so only decoys in that zone could be relevant. Besides, not all ASM are radar guided (NSM has IR seeker, and future missiles could follow this path). That said: some decoys are not a bad proposition... but I will also invest money in trying to detect and destroy the supplier of the info (satellites, enemy MPA) for the sub, which will be forced to surface some antennas to allow those communications (its antennas should be detectable once in the surface of the sea).
      NOTE: re-reading your 7th point -> I think that no enemy submarine will launch ASM to a zone only for what teir passive sensors tell... because passively you can't tell distances accurately (for what I have read until now).

      2) Acoustic detection under water is tricky. If it was as easy as turn on the sonars and "see"... then everybody will use cheap deep-charges to destroy all submerged threads... and that's not the case. Perhaps LIDAR (https://www.dsiac.org/resources/dsiac_journal/scanning-underwater-smaller-lidars-and-uavs) could allow to see clearly under water -also subs?- at a good enough distance, but to turn on low frequency sonars very loud... I think that is not a good enough solution... that could give very bad collateral damage.

      3) MPA launch a series of sonobuoys that can dip (or not, depends on the sonobuoy launched)... and communicate what their sensors detect to the ASW aircraft. It processes signals and can decide how to act. All this is done faster and in a wider zone than an ASW helicopter could dream... and with a lot less risk for the aircraft (low flying stationary helicopters are "easy prey").

      MPA only drawbacks (that I can think now): price and that later you should send a helicopter to "recover" all the stuff launched (or a vessel with UUV/divers if there was engagement with a sub-sea explosion and you can investigate the submerged hull).

      By the way, thinking about specialized ships to investigate under water: probably not only surface ships and submarines are objectives for enemy submarines... I am also thinking in submarine communications cables.

      UUV) The fastest investigation of submarine contacts... for now it's a MPA job (that also could detect antennas of enemy submarines and ASMs). UUVs are for "stealthy operations" or for acting as decoys (underwater communications are very limited).

    3. 1) Even tiny, weak airborne radars can detect cargo ships at about 70 km. Without decoys some SSG could simply launch 20-30 missiles programmed to fly along the corridor and look for targets to engage. There would be 10-20 hits (my guess). With decoys still 4-10 hits (same).
      Convoys - if employed in the corridor at all - could be heard by submarines from 100+ km and engaged with some precision.
      So without decoys one would need to provide serious (expensive) air defence instead of merely keeping submarines out of the corridor. This would mean AEW, CAP, possibly AAW FFGs ... several billions Euro higher expenses per 100 nm corridor length.

      2) Even blue lasers have a marginal range in water. The dissipation and absorption are too high.

      3) ASW helicopters can use sonobuoys as well, but their monopoly is on hovering (or floating) and employing an actual dipping sonar.
      Typical ASW aircraft such as P-8 cannot do so, even flying boats couldn't do so unless the sea is calm.

      The final identification of silent active sonar contacts could be with imaging sonar, which requires getting close. A high seas-capable speedboat with a tethered imaging sonar drone might work, but in heavy sea states a helicopter might need to be dispatched.

    4. 1) I still doubt that a sub will launch the "few" ASMs that can operate without confirming and reconfirming their target and location. But if you think that enemy submarines will be so aggressive: then yes, we will need acoustic and radar decoys. Perhaps we should consider also to be aggressive --> point 2) in http://www.usni.org/magazines/proceedings/2014-06/hunt-full-spectrum-asw

      3) When you are using multiple sonobuoys you are using a multistatics approach in ASW... that probably is better than a monostatic one (even if that one is a low frequency active sonar diping very, vey loud (it's what I think after reading http://www.ultra-ms.com/pdfs/Multiplying%20the%20Effectiveness%20of%20Naval%20ASW.pdf ). A (good) MPA can launch and control a lot more sonobuoys than an ASW helicopter (it has more room and power capability -to install computing capability-).

      I have also read a CSBA report: "THE EMERGING ERA IN UNDERSEA WARFARE" (it shows that ASW is always evolutioning) . I think that there should be a compromise for ASW. Something like what exists today in AAW (with Aegis ships -usually in "silence" to no give their position- + AEW aircrafts). So, for ASW: ships towing sonars should be passive by default, while MPA will have its sensors always active to detect snorkel/antennas/wakes...

      The tricky part will be to determine when, where and how those MPA will launch its sonobuoys and the towed sonars should be activated... in order to "create doubts" in submarine´s commanders (if doing those actions a sub is detected and can be engaged... well, but the mission is to defeat the submarines -as in the first link of this reply- ).

      About imaging sonar ) I would like an UUV with that capability... and being air-deployable (MPA and/or ASW helicopter) the contacts could be identified quickly.
      NOTE: That UUV could have a second function: to "recover" all sonobuoys launched in the zone and then wait until "some ally" can "recover" her. Perhaps an USV (= more payload than UUV) could also do a good job, but probably it should be semi-submergible in order to be enough "all-weather".