The Economist - USA (2022-01-29)

8 TechnologyQuarterlyDefencetechnology TheEconomistJanuary29th 2022

merous, they might be able to do more detecting themselves. The

sensors available for such arrays have improved greatly, according

to Bryan Clark, a former submariner now at the Hudson Institute,

a  think­tank  in  Washington.  New  solid­state  “vector”  sensors

measure the velocity and acceleration of water molecules, which

means they get more information out of a sound wave than a sim­

ply  pressure­sensitive  hydrophone  does.  The  signal­processing

systems required to discern a submarine’s screw in the din of the

ocean are improving even more quickly. 

They are also shrinking. Ken Perry, a retired rear­admiral and

vice­president of ThayerMahan, a Connecticut­based firm which

builds  maritime­surveillance  platforms,  recalls  a  time  when  so­

nar  computers  were  so  large  and  inefficient  that  submariners

warmed up their coffee on them. Now a surfboard’s worth of solar

panels can run them and still provide enough juice to transmit the

information thus produced. Hence the interest in things like Wave

Gliders  and  ThayerMahan’s  rather  larger  usvs,  which  carry  ten

times the payload capacity and move a lot quicker. 

A fleet of array­towing usvs could cover millions of square ki­

lometres of ocean for “a fraction of the cost of a single frigate or

submarine”, says Mr Perry, whose company has tested the concept

in exercises with America’s navy. The bit of the Pentagon charged

with pushing technological boundaries, darpa, is working on an

“Ocean  of  Things”  project  which  would  contain  thousands  of

“low­cost  floats...that  drift  as  a  distributed  sensor  network”.  The

idea  is  that  armadas  of  prowling  hydrophones  could  eventually

plug into a wider network of sensors, including fixed arrays, sono­

buoysdroppedfromtheairandautonomousunderwatervehicles

(auvs)—dronesubmarines.

Anotherdarpaprojecthasworkedonnewwaystofollowup

suchdetections.In 2016 itproducedausvcalledSeaHunter, a ro­

botprototypedesignedtofollowa submarineforthousandsofki­

lometresentirelyautonomouslywhilerespectingalltheinterna­

tionalrulesdesignedtoavoidcollisionsatsea.Suchvessels,a lot

biggerthanmostsurfacedronesbutmuchsmaller,andfarcheap­

er,thana frigatewitha crew,couldintheorybedeployedinfairly

largenumbers,andincontestedwaters.

WhateverhappenedtoJonesy?

Anoceanthatissuffusedwithsensorsaboveandbelowthesur­

faceandwhichhassub­trackingrobotsontheprowliscertainlya

moreinhospitableplacefora submarine—oratleast,foronethat

doesnotbelongto Americaor oneofitsallies.Floodingthe

world’soceanswithsuchsensorsissomethingonlya greatpower

cando.Asfarasmostpeopleareconcerned,saysMrCote,“the

oceansareopaque,andwillprobablyremainso.”

Changingthiswouldrequiresomenewtechniquetosupple­

mentwhatisavailable,andthereislotsofresearchondetecting

magneticdisturbancesandveryfaintwakes,sniffingouttelltale

chemicalsorradiation,andpingingtargetswithlaserstunedto

theblue­greenwavelengthswhichbestpenetrateseawater.Some

ofthesetechniquesmightworkbestunderwater.Picturesofcuri­

ousappendagesthatmightholdsensorsofvarioussortsonsub­

marinescomingintoorleavingportreliablysparkdiscussionin

thesub­curiouspartsoftheinternet.Otherscouldbedeployed

fromaerialdrones,andthuscouldbeusedalotmoreifsuch

dronesbecamemorenumerous.Butshortrangeslooklikelytore­

maina problemforallthesemethods,asdoesthefundamental

challengeofseparatingsignalfromnoiseinbigmessyoceans.

Andsubmarinerscouldfightback,notesDavidBlagdenofthe

UniversityofExeter.A submarineleavingportmight“delouse”it­

selfofinquisitiveusvs byusingtechnologyasrudimentaryasa

tugboatandropenetting.Shouldwakedetectionshowpromise,

submarinescouldsimplyheadtorougherseas.Thelow­power

transmissionsfromusvs tosatellitesornearbywarshipscouldbe

jammedbyotherusvs,orbydrones.

The last of those tactics speaks to a perennial problem for anti­

submarine warfare. The oceans do not just make it hard to gather

information; they also make it hard to pass it on. Sensors which

spend all their time submerged have either to be hard wired to ca­

bles  or  to  communicate  using  acoustic  modems  that  are  slow,

cumbersome and limited in range. This is a real bottleneck for sys­

tems trying to make use of auvs. 

This requirement for cables on the sea floor makes geography

important.  Navies  fight  above  the  seabed  they  have,  not  the  one

they would like. In the North Atlantic, America enjoyed the advan­

tage of laying its cables in very deep water—inaccessible to all but

highly  specialised  submarines—and  then  up  a  continental  shelf

that rose, sharply, on to allied territory. By contrast, if China want­

ed to assemble a sonar net across the Philippine Sea, it would have

to lay fibre­optic cable all across the South China Sea, bits of which

are shallow enough that cables there are frequently cut by fishing

vessels. Those cables would be at the mercy of foreign navies. .

That could make it hard for China to stop submarines getting

close to its shores. And sonar systems at choke points like the Lu­

zon  Strait  could  make  it  difficult  for  Chinese  submarines  to  slip

into the open ocean. Both constraints would be to its disadvantage

in wartime. But they would not render its ssbns useless. Such sub­

marines do not need to be able to prowl every ocean with impuni­

ty. They just need an area within range of their missiles’ targets but

out of bounds to other navies and their sensors—what navies call a

“bastion”. Seeing through an ocean will be hardenough if you have

access to its surface and its depths. Seeing througha sea you can be

kept out of is a different kettle of invisible fish.n

3mWaveGlider

20mSeaGuardian(UAV)

Variable

depth

sonar

Source:The Economist

40mSeaHunterfromDARPA's

ASWContinuousTrailUnmanned

Vessel(ACTUV)project

150mVanguard-classsubmarine(SSBN)

2.m

AutonomousUnderwater Vehicle (AUV)

150m Type 2 frigate

Sub-huntinghelicopter

Welcome to the new world, Captain

Selected platforms for anti-submarine warfare

By length, metres