FixedNavalDefencesinDarwinHarbour1939-1945 by PatForster

� BoomJe0yandYardFortHill. Betweenlate1941andearly1942Darwinunderwentasignificantmetamorphosis,rapidlyemptyingofciviliansandbecominganalmostsolelymilitarytown.Yet,withtheendofhosGliGesthesituaGonjustasrapidlyreversedandmuchofthedetailofDarwin'swarGmehistorywassoonforgo0en.

� MapofDarwinHarbour. AnumberofpublicaGonstellthestoryofthewarinNorthernAustralia,buttheydealmainlywithacGonsorevents.Detailsoffixeddefenceshaveeitherbeenomi0edormenGonedonlyperipherallyalongwithaparGcularincident.ThiswasthecasewithDarwin'sHarbourdefences.

Today,manyDarwinianswillproudlytellyouthatananG-submarineboomnetthatstretchedacrosstheharbourwassixkilometreslong,andthelongestfloaGngnetintheworld.But,veryfewofthemeversawtheflotaGonbuoysthatsupportedthenet,andfewersGllknewwhatwasbelowthesurfaceofthewater.Similarlyunknownwerethesubmarineindicatorloopsthatlayontheseabedandwarnedofapproachingshipsorsubmarines,andthepartplayedbyASDIC(Sonar),fi0edtoshipsinthedefenceofDarwinHarbour. ThisarGclea0emptstothrowsomelightontheanG-submarineboomnet,theindicatorloops,ASDICandthePortWarSignalStaGon(PWSS)atDudleyPoint,allofwhichplayedavitalpartinthedefenceofDarwin. DefencesPlannedforDarwinHarbour In1937internaGonalpoliGcaltensionsweresuchthatanotherWorldWarseemedinevitable.BritainneededharboursforherEasternFleetandselectedDarwinandCockburnSound,southofFremantle,WesternAustralia,aslikelybasesforsuppliesoffuel,waterandstores.LaterthatyearHMASMoresby(I)surveyedDarwinHarbour,andtheresultsofthissurveyrevealedthatitcouldprovideafleetanchoragesuitablefor28shipsand17smallcra]intheMiddleandEastArms. Inamemocirca.1939theAdmiraltyannouncedarequirementforsingleberthanchoragesforoneba0leship,oneaircra]carrier,threecruisersandeightdestroyers.AnchorageswerealsorequiredtoaccommodatethenumerouslocaldefencevesselscomprisingfourFairmiles(smallversaGlewoodenhulledvesselsmass-producedinAustralianyardsandusedforpatrolwork),fourHarbourDefenceMotorLaunches(HDML),threeminesweepers,twoBoomGateVessels(BGV),fourBoomWorkingVessels(BWV),sixchannelpatrolboatsandoneexaminaGonvessel. In1938theAdmiraltysentanexpertonharbourdefences,CommanderBannisterRNtoAustraliatoadvisetheNavalBoardonnecessarydefenceprocedures.TheAdmiraltyundertooktodesigntheanG-submarinedefencesforDarwinwhiletheAustralianNavalBoardiniGatedtheconstrucGonoftwoBWVsthatwouldbeneededtolaytheanchoragefortheboomnetandsubsequentlymaintainit. ThefirstvesselbuiltwasHMASKookaburra(I)whichwasbasedontheRoyalNavy's'Net'Classdesign.Thesecondvessel,HMASKoala(I),wassimilartotheRoyalNavy's'Bar'Classdesignandwas40feetlonger(178.3feet)displacinganextra300tonstothatofthe'Net'Class.Thetwo

vesselswerecompletedinearly1940withathirdvessel,HMASKangaroo(I),arrivinginDarwininJanuary1941followedbyafourthHMASKarangi(I),inJanuary1942.

� HMASKookaburra.

� HMASKoala. By1942theboomservicehadalsobeenallocatedfiveBoomDefenceVessels(BDV)thatwerenecessaryforpatrollingtheboomnet.ThesevesselsconsistedofformermotorboatsandmotoryachtsthatwererequisiGonedforthispurpose.ThevesselswerearmedandputintoserviceasHMAShipsKuru,Kiara,Vigilant,MoruyaandLarrakia,performinggeneralboomdefenceandairsearescueduGes. In1938LieutenantCommanderW.HThurlby,RANandMr.G.DLogan,aciviliandraughtsman,travelledtotheUKtobepresentwhiletheplansforDarwin'sboomdefencewerebeingdrawnup. TheyalsospentGmeattheAdmiraltyandvisiGngvariousboomdepots.OntheirreturntoAustraliain1939,LieutenantCommanderThurlby

becameOfficer-in-ChargeofBoomServicesforAustraliaandhewaslaterappointedastheDirectorofBoomServices.InthiscapacityhesupervisedthepreparaGonforthelayingoftheDarwinanG-submarineboomnet.ThatsameyearChiefPe0yOfficerWrightfromtheRoyalNavytransferredtotheRANandwaspostedas'Chargeman'inDarwin.InthiscapacityhetrainedcivilianriggersinnetmakingandalsogaveadviceonsteelwireropefabricaGon. InOctober1939,LieutenantCommanderA.E.Fowler,RAN,atthatGmeDarwin'sChiefofStaffattheFortressCombinedOperaGonHeadquarters,wasappointedtheBoomDefenceOfficer,Darwin.Togetherwithfourseniorsailors,FowlertravelledtoSingaporeearlyin1940wheretheystudiedandtrainedinboomdefencemeasures. TheyreturnedtoDarwinon14April1940wheretheywerejoinedeightdayslaterbyLieutenantCommanderThurlbyandMrLogan.LecturesonlayingboomnetsweregiventoofficersandraGngsfromKookaburraandKoalaaswellasthepersonnelwhohadassembledinDarwintoworkontheboomdefencefaciliGes.Thesecomprisedchargemen,riggers,arGsans,skilledlabourers(leadingseamen)andlabourers(ableseamen).InOctober1940approvalwasgivenforwivesandfamiliestojointheriggerssubjecttotheavailabilityofaccommodaGon. LieutenantCommanderThurlbyle]Darwinon20May1941andLieutenantCommanderFowlerassumedresponsibilityforthelayingoftheboomnetanditsongoingmaintenanceunGltheendofthewar. ThewireropeusedforthenetswasmanufacturedbytheAustralianWireRopeWorksatNewcastle,NSWanddifferedfromnormalwirerope,whichhadacore.Thehightensilewireropeusedfortheboomnetswasaboutoneinchindiameterandconsistedofallwirestrands.Thatusedforthejackstayalongthetopofthenetwas2inchesindiameter. Thelayingofthenetwasscheduledtobecompletedbytheendof1940.However,duetothepreparaGonrequiredfortheassemblyofthenetintheboomyard,thelayingofthemooringsandunforeseenproblemscausedbyGdalcondiGons,thelayingofthenetdidnotbeginunGltheendof1940andwasnotfinishedunGltheendof1942. ThedelayssignificantlyincreasedthecostsoftheprojectastheFirstNavalMember,AdmiralSirRagnarColvin,notedinaminutedated22May1940: IconsiderthatweshouldnowtakestockofthesituaGonwithregardtoourcommitmentsontheboomdefencesatDarwin.Thecostwas

originallyesGmatedoftheorderof£600,000.Ithasnowreacheddoublethat-over£1,200,000-andthelimitisnotyetinsight.TheextensionstotheboomadvisedbyAdmiraltyandtheaddiGonalvesselsmayeasilyentailanother£500,000ormoreandtheeventualtotalcapitalcostmayquitelikelybenotlessthan£2,000,000.TheprojectinmyopinionhasassumeddimensionsofamagnitudeoutofallproporGonnotonlytotheothersea,landandairdefencesofDarwin,buttoourtotalnavaleffortandexpenditure. Beforeworkonassemblingthenetscouldbegin,alargeboomshedhadtobebuiltintheboomyardnexttoFortHill.

� BoomYard,1942onwards.

� BoomYard,1940.Photo:PeterandSheilaForrest.

� WithintheBoomYard,1942.Sketchfrom'TheNavyinDarwin1942-1943'.CourtesyofMAGNT.

� WithintheBoomYard,1950.Photo:PeterandSheilaForrest. InApril1940abranchlinefromtherailwayyardswasrunalongtheshorelinetotheboomshedtotransporttheheavycomponents-buoys,wireropeandchains-arrivingbyshipattheStokesHillWharf. By1October1940workontheboomdepotwasvirtuallycompletewiththeexcepGonoftherailwaybranchlinesthatwererequiredtobelaidacrosstheyard.AroundthisGme,partofFortHillwasalsodemolishedtomakeroomforaroadandworkspaceattheendofthenewconcreteje0ybeingbuiltbyHornibrookandCo.ThiswasnotcompletedunGlmid1941.Aconcretenetslabonwhichthenetsweretobemadewasalsopouredneartheje0yandwasreadyforusebySeptember1940.AfurthernecessitywastheneedforaconcretelaunchingtroughdowntothewaterthatallowednetstobeslidintotheharbourandthentowedouttotheboomnetlocaGonbyoneoftheboomworkingvessels. TheDepartmentofInteriorinDarwinpouredtheconcreteslabandmadethelargefiveandeight-tonconcretemooringclumpsusedfortheanchorageoftrots.

� 8tonconcreteclump,detailsofsteelwork.

Trots Trotswereanassemblageofthreecylindricalbuoysanchoredbyeight8or5tonconcretemooringclumpstotheseabed.FourclumpswereposiGonedontheseawardsideofthenetandafurtherfourwereposiGonedontheharboursideofthenet.Thetrotbuoysweresecuredtotheclumpsby1½"or2"chaincable.Inspecialcasesalargepegtopbuoywasusedinsteadofacylindricalbuoy.Fortheanchorageofthetrots,230tonsof1½"chaincablearrivedfromAmericainJune1940.Inall,theboomnetmooringsused265clumps.

� FinalLay/OutofA/SBoom. Arecordof8May1939liststhecostof70five-tonconcreteclumpsmadebytheDepartmentofInterior,Darwin,asbeing£1500. • Eightfootmesh-300]x91] • Threefootmesh-297]x93] • Netmadeinthreedepths,25],55]and93]. • DistancebetweenTrots-195yards • NumberofTrots-30 • Photographicevidencesuggeststherewere20to22flotaGonbuoys

oneachnetsecGon.

TheNet Themanufactureofthe8-footmeshnetsconformedtotheUKpa0ern.On30September1939thefirstitemsfortheboomdefence-thecylindricalbuoys-arrivedbyship.ThesewerefollowedinMay1940byforty-nineanG-submarinenetsvaryingfrom2½tonsto7tons.Becausetherewasnocraneintheyard,thesenetshadtobemanhandledfromtherailtrucksintotheboomshed.Thefirstnetsusedcamefromthe

AustralianWireRopeWorks,buta]erSeptemberthenetsweremadeintheboomyard. Theconcreteslabonwhichthenetsweremademeasured320feetby106feetandwasmarkedoutwith27holes,11feet3¾inchesapartalongthelongside(top).Eachsidehad17holes,5feet7and7/8inchesapart.A1½inchgalvanisedpipeaboutsixincheslongwassetintotheholes.Intothesepipesan18inchlonggalvanisedpipe1¼inch(externalmeasurement)wasfi0edandlooseenoughtoberemoved.ThepipeswereposiGonedtoindicatewherethewireropesstartedtheirdiagonalpa0ernovertheslab.Whereropescrossedtheywereshackledtogether.Speciallydesignedshacklesheldtheropesatrightangles. Thetopofthenetwasshackledtothejackstay,(alengthofsteelwireropestretchedbetweentwopoints).Therope300feetlonghadhardeyessplicedintoeachend.Afour-footlengthofchainwasshackledtoaringundertheflotaGonbuoysandtheotherendofthechainwasshackledtothetopjackstay.FlotaGonbuoyswerespacedapproximatelyevery15]alongthejackstay.

� PosiGoningtheNet. ThenetwasthengathereduptothejackstayandGedatintervalswithwireropestoppers.Thiswastopreventthebo0omofthenetdraggingalongtheseabedandbecomingsnaggedonreefsorrocks.

Oneendofthejackstayfacedthelaunchingrampandan9tondiesellocomoGvejibcranethatranontheraillineadjacenttothenetslabwasusedtodragthenettotheheadofthelaunchingtroughwhereitwassecuredtoaropefromaboomworkingvessel.ThevesselhauledthenetwithitsflotaGonbuoysintothewaterandtoweditoutintoposiGon. TosecurethesecGonofnetbetweenthetrotseachendofthejackstaywasshackledtoaringbeneathoneoftheouterlargecylindricalbuoys. Whenthenetwassecuredbetweenthetwotrots,ariggerwouldmovealongthetopofthenetandcuttheGeswhichheldthenettothejackstay.Toworkonthemooringchaincableunderthebuoy,itwasnecessarytoli]thebuoyoutofthewaterundersideup.Alassowasmadefromawireropeafewfeetlongerthanthecircumferenceofthebuoywithaso]eyesplicedintoeachend.Thiswasshackledtoaso]eyeonawireropefromtheship'swinch.Arigger,balancingonthebuoy,slippedthelassoovereachendofthebuoyanditwasthenwinchedin,li]ingitoutofthewater.

� Li]ingBuoy.NorthernTerritoryLibrary,RonUrquhartCollecGon. WhentheoperaGonwascompletedthebuoywasloweredintothewater,thelassowasslackenedandthewinchwireunshackled.Theriggerthenswamunderthebuoytoeasethelassoloosefromthechaincable.Thisallowedtheriggertothenretrievethelasso.

Later,duetothethreatofmidgetsubmarineandhumantorpedoa0acks,theAdmiraltyorderedthesizeofthenetmeshtobereducedto3feet.Fortunately,noalteraGonwasrequiredtobemadetotheDarwinnetslab,astheAdmiraltywasabletosupply3.48milesof3]netfromstores. LayingTheTrots InNovember1940,transitmarkerswereerectedatanalcove500feetnorthofDudleyPointandatWestPoint.Kookaburra,starGngwithtrotoneontheedgeofashelfthenlaidmarkerbuoys(44gallondrums)betweenDudleyPointandWestPointtoindicatethelineformooringthetrots.Oncethemarkerbuoyswerelaidandtheworstofthewetseasonhadpassed,Koalabeganlayingthemooringsforthetrots,anoperaGonthattooktwomonths. Trots1-12and14-18werelaidby9April1941.Aspacefortrot13wasle]opentoallowforashippingchannel. TheriseandfalloftheGdecouldo]enexceed20feetandthestrengthoftheGdalstreamcausedunforeseenproblems.DuringJulyandAugust1941mostofthemooringsbetweentrots5and20movedandhadtobeli]edandre-laid.InOctobertheIndianSpringTidecausedtrots11-14tobreakawayfromthemooringswiththeneta0ached.Thestresscausedontheclumps,thechaincable,thewireropeandtheshackleswassostrongthatmanycomponentshadtobereplacedandconsequentlytheclumpswerere-designedtotakethestrain. AnRANsurveyconductedinAugustandSeptember2005revealedtheconGnuedexistenceofthe8tonconcretemooringclumps,andotherassociatedfisngs,le]ontheseabedin1945.Thesurveyalsoindicatedthattheseitemshavebeensubjecttosomemovementoverthelast60years. LayingtheBoomNet Thenetwasatfirstlaidfromtrot22onthewesternsidetotrotG.LateritwasextendedtotrotHatthebeginningoftheshelfoffDudleyPoint.Unfortunatelythisle]astripofunprotectedwateratbothendsofthenetwhichathighGdewouldbedeepenoughtoallowenemymidgetsubmarinesandmotortorpedoboatstopassaroundtheendoftheboomnet.ConsideraGonwasgiventobuildingabreakwaterateachendoftheboomnetbutthisideawasdismissedwhenthemorepracGcalsoluGonoferecGngsevenpylonsontheeasternsideoftheharbourtospanthe1866

feetofshallowsandreefstotheDudleyPointcliffswassuggested.SimilarpylonswereerectedintheshallowsatWestPoint. Photographicevidencesuggeststhatthepylonswere25feethighwithconcretefoundaGonsonthereef.AtwoinchwireropeconnecGngthetopsofthepylonspreventedforeanda]movementandsidestayspreventedlateralmovement. AnetwashungfromthewireropelineshangingfromthejackstayconnecGngthetopsofthepylonswiththeeasternendofthejackstaybeingsecuredtoaconcreteblockonthecliffatDudleyPoint.ItwasesGmatedthatitwouldbeJune1944beforetheseaddiGonswerecompleted.AnecdotalevidencesuggeststhatthepylonsweredestroyedusingdemoliGonchargesin1967or1968.

� PylonWestPoint.NTLibraryWoodrowCollecGon.

� RemainsofpylonsexposedatlowGde.

TheGateandtheGateVessels Toenableshipstoenterandleaveharbour,twopermanentlymooredgatevesselsoperatedagateinthenetwithintheshippingchannel. InNovemberandDecember1940,withtheassistanceofa10toncraneanda60tonlighterfromHornibrooks,five-tonconcretemooringclumpswithchaincablewerelaidontheseabedtoprovidemooringsforthegatevessels. HMASKaraKara(I)andHMASKoompartoo,twoformerSydneyferries,wererefi0edandcommissionedforthispurpose.Thisincludedequippingthemwithpowerfulwinchesontheira]erdeckstoenablethemtooperatethegate.KaraKaraarrivedinDarwininNovember1941andwhileKoompartoowasbeingconvertedKookaburraandHMASGunbar(I),

anauxiliaryminesweeper,alternatedasgatevessels.KoompartooeventuallyarrivedinDarwininFebruary1943.

� BoomgateoperaGondiagram. DuringtheoperaGonofopeningthegate,thea]erdecksoftheKaraKaraandGunbarwereclearedofallpersonnelexceptfortheEngineRoomArGficer(ERA)operaGngthewinch.WhentheGdewasflowingstronglytherewasenormousstrainontherecoverywireropeandoccasionallyitwouldpartbetweenthesternandthegate.Releasedofitstensionthelooseendofwireropewouldswingwildlyintheairandoverthedeckforseveralseconds.TheERAwouldhavetoduckforshelterbehindthelargedrumofthewinchtoavoidthewirethatwouldhavecutinhalfanyoneonthea]erdeck. Atfirststoresandwaterforthegateshipsarrivedregularlybyatowedlighterorbyoneoftheotherboomworkingvessels.Lateraregularservicewasprovidedbyasupplyvessel.KaraKaraandKookaburrawereplacedinthegateinJanuary1942andthegatebecamefullyoperaGonalon14February1942.Asmallgate,largeenoughforpatrolboatsandluggerstopassthrough,operatedbetweenthestarboardsideoftheeasterngatevesselandalargepegtopbuoy.

� HMASGunbarasseenfromthedeckofHMASKaraKara. Duringthe19February1942Japaneseairraids,bothgatevesselswereheavilymachinegunned.KaraKarasustainedcasualGes,withhercaptainandfourofhercrewbeingbadlywounded.TheinjuredweretransferredtotheHospitalShipManunda,whichsailedforFremantlethefollowingdaywith300otherwoundedpersonnelonboard.ThegatewasconsequentlyclosedunGl13March1942.Whenthegatereopened,Gunbarwasassignedasthewesterngatevessel,unGlKoompartooarrived,andKaraKarawasassignedastheeasterngatevessel.

� HMASKaraKara.

MaintenanceoftheBoomNet

� BoomDefenceraGngbadge. Theboomworkingvesselswereconstantlyrequiredtocheckandreplacedamagednets,shacklesandbuoysthathadbrokenadri]orweretakinginwater.ThisworkwascarriedoutbyRiggers.TheirduGeswereseparatefromthenormal'partofship'duGescarriedoutbyothermembersoftheship'scompanywhichincludedpainGng,chippingrust,gunnery,watchkeepingetc. 'Riggers'wasthegenerictermusedtodescribethemenworkingontheboomnetando]enasmanyassixwouldbeassignedtoeachboomworkingvessel. Thenavy'sraGngequivalentwas: Chargeman

ChiefPe0yOfficer Riggers Pe0yOfficersandLeadingSeamen SkilledLabourers AbleSeamen Labourers OrdinarySeamen TheriggersweresupervisedbyaPe0yOfficerand/oraLeadingSeaman,andfortheirhazardousworktheyreceivedanextraoneshillingadayasdangermoney.Aswithmostship'scompaniesinthetropics,ahardlyingallowanceofoneshillingadaywasalsopaidtothem.(Theequivalentof1/-in1945isabout$7.50in2006).Hardlyingallowancewaspaidtoship'scompanieslivingintheexcepGonallyuncomfortablecondiGonsthatexistedinthetropicsthatmadesleepingincrampedmessdecksbeneathanirondeckhead(ceiling)quiteunbearable. AbleSeamanDaveGooden,anex-rigger,providesaninteresGnginsight,throughhisrecollecGons,intothedaytodayacGviGesoftheriggers'...wewerevolunteersandcouldnotbeorderedovertheside,butsuggesGonsweremadethat'soandso'shoulddo'thisorthat'andusuallytherequestwascompliedwith.Butwewerenever[asked]unlessthePe0yOfficerthoughtwecouldsafelyhandlethejob.'

� Riggersworkingonthenet.TheAustralasian1943. 'Thejackstayonthetopofthenetwashauledupbyagrapnel(athreeorfourprongedhook)tothehornsontheboomvesselandtheriggerswouldworktheirwayalongthejackstayintothewaterandswimfrombuoytobuoy.Weonlyworeshortsandheavybootstoprotectourfeetfromthebarnaclesandourhandsbecamecallused.[Someworeleathergloveswiththefingerscutofftoprotecttheirhands].Thewireropesandchainswerecoveredwithbarnacles,whiteslimysealice,seaweedandsponges.Forsafety,alookoutwaspostedontheshiptokeepaneyeoutforsharks.' AbleSeamanBertJones,anotherrigger,recallsthat,'whenrepairingandGghteningtheshacklesontheflotaGonbuoys,aspanner[onalanyard]wasa0achedtoourwaist...'healsorecalls'theinfecGonwereceivedfromfrayedwires'aswellas'awatch(lookout)]beingpostedondecktowarntheriggersonthenetofdri]ingjellyfish[BoxJellyfish].Theyweren'tdifficulttosee.ThewaterwascrystalclearandyoucouldeasilyseeaswarmfloaGngabout2]fromthesurface.' ANavalmedicalreportof19July1945,confirmsatleastfourcasesofswimmersbeingstungbyBoxJellyfish.Allweresuccessfullytreatedatthehospitalhowevernonewereriggersworkingontheboomnet.Another

ex-rigger,ArthurLorriman,recallsa0endingafuneralinearly1944forAbleSeamanW.N.SchneiderwhowasfatallystungattheLamerooBaths. RiggerswerealsoconGnuouslyemployedintheboomyardsplicingwirerope,construcGngnets,chippingrustoffbuoysandrepainGngthem. ThemostfrequentlyusedbuoyswerethelargecylindricaltypeusedforthetrotsandthebarrelshapedflotaGonbuoyssupporGngthenets.Pegtopbuoyswerealsousedtosuitspecialcircumstances. IllustraGonsarenottoscale.

� Detailsofcylindricalbuoys.

� Buoymaintenance.NAA150/1.

CompleJonoftheAnJ-SubmarineBoomDefence Withtheboomnetandextensionscompletedin1944KarangiwasreleasedtodoworkinotherportsbutKookaburra,KoalaandKangaroowereconstantlyatworkmaintainingthenetandthemooringsunGlitwasGmeforthemtobedismantledfollowingthecessaGonofhosGliGesinSeptember1945.

IndicatorLoop

� SubmarineIndicatorLoopconstrucGon. NumerousmethodshadbeendevelopedpriortoWorldWarIItoalertharbourdefenderstothepresenceofenemysubmarinesanditwasmagneGcsensingthatwasselectedforanG-submarinedetecGonatDarwin.ThismethodreliedontheproducGonofaninducedcurrentinastaGonaryloopofwireplacedontheseabedthattriggeredasignalwhenashiporasubmarinepassedoverhead. TheRoyalNavydevelopedthetechnologyin1915atHMSOsprey,whichtheylatersharedwiththeUnitedStatesNavy(USN).ThefirstrecordeduseoftheIndicatorLoopswasatScapaFlowonthe28October1918whentheGermanU-BoatUB-116wasdetectedanddestroyedinacontrolledminefield. Thecablethatactuallydetectedthecrossingsconsistedofasinglecoreof17strandsof.029inchesGnnedcopperwirecoveredwiththreelayersofIndiarubberthenalayerofwaterprooftapewoundwithjuteyarn.Thiswasthencoveredwithhessiantapeandspirallywoundwithso]leadalloywire.Theleadwascoveredwithmorewaterprooftape,atarredjute

serving,twomorelayersofhessiantape,22steelarmourwires(each2mmdiameter)coveringthelead. Furtherbraidingofdressedhempyarnwrappedoverhotpitchandresinwasadded,andfinallyapreservaGvecoaGng.Thefinaldiameterwas1.3inches(33mm)anditweighed6.09tonspernauGcalmile. Theloopwastypically5000ydslongand400ydswidewithacentralcablerunningthelengthoftheloopandjoinedatbothendsbyawaterproofjuncGonbox.FromthejuncGonboxatoneendatailtravelledtheseabedtotheshoreandanIndicatorloophut. Thelooptailwasa4core,7strand.029inchcableusedforthefourcentralcoresandhada22strandsteelcablearmour,withafinaldiameterof25mm. (ExtractsfromWalding,Richard.IndicatorLoops,MoretonBayCollege,Wynnum,Queensland).

� PosiGonofIndicatorLoops. InSeptember1940twoIndicatorLoopswerelaidtwomilestotheseawardsideoftheDarwinanG-submarineboomnet,requiringsome276,000feetofcablesuppliedbyCableandWirelessLtd,VictoriaEmbankment,London. Unfortunately,theforceofwatercausedbythechangingGdesandtheroughseabedinDarwinresultedinmanybreakagesinthecable.Followingasurveyconductedoftheseabed,byHMAShipsVigilant,KiaraandWato,itwasdecidedtolayareplacementoffiveloopsthreemilesfurthertoseaward.Thiswascompletedin1943whentheindicatorloop

hutwasmovedtoNightcliff,westofthepresentje0y,providingamoredirectlocaGonforthetailsfromthejuncGonboxestotheshore.ThehutwasfullyoperaGonalon30June1943. BetweenJanuaryandMarch1942,severalunsightedcrossingswererecordedbytheindicatorloop.Later,between8and16Augustthatyear,unsightedcrossingsweremadeandthesignaturesrecordedonthescreeninthehutwereverysimilartothosemadebythemidgetsubmarinesthatenteredSydneyHarbourinMay1942. SecurityfortheindicatorloopequipmentatthestaGonwasconsideredparamount.ShouldtheJapanesehavelandedinDarwinitwouldhavebeenimpossibletoretrieveanyofthecablefromtheseabed,butwithoutthereceivingequipmentitwouldhavebeenuselesstoanyone.On21August1941ale0erfromtheNavalBoard(1855/3/185)instructedallindicatorloopstaGonstoprepareplansforburyingtherecordingequipment,whichwastobedistributedinthreeboxes.Advicemarked'MostSecret'wastobesenttotheNavalBoardshowingtheburiallocaGonthatincludedadiagramwithbearingsanddistancesfromaknownposiGon. Asdic(Sonar) ThisdetecGondeviseiscommonlyreferredtobyitsacronym'ASDIC'[AnG-SubmarineDetecGonInvesGgaGonCommi0ee].Similartoahydrophone,anasdicmadeuseofunderwateracousGcs,butwasbasedonhighfrequencyechoranging,andhencewasanacGveratherthanapassivesensorsystem.Itcouldbefi0edaspartofaharbourdefence,buttheNavyexpectedASDIC'sprimeapplicaGontobeinsurfacevessels.Thedeviceconsistedofanoscillatorbuiltupofquartzdiscsandfi0edinacircularsteelframe.Inuse,theoperaGngvesselsloweredtheoscillatorthroughatrunkopentotheseaunGlitprotrudedbelowthehull.Protectedfromdamagebyadome,theoscillatoractedbothastransmi0erandreceiver.Sincethespeedofsoundwasknown,thetarget'sdistancecouldbemeasuredbytheGmeittookfortheechotoreturntothesource.TheasdicoperatorcouldalsotraintheoscillatorinahorizontalplaneandthusthecombinedsystematlastmadefeasibletheaccuratelocaGonofasubmergedsubmarineintermsofbothrangeandbearingfromtheequipment. TheRoyalNavyfi0edthefirststandardasdicset,Type112,insomeofthePortland'P'boatsin1920...earlyexperimentsingoodcondiGons

produceddetecGonrangesof3000-4000yards.AssumingtherealisaGonofthefullpotenGal,ASDICclearlyofferedascienGficdevicesoeagerlysoughtbytheAdmiralty...[and]providedtheidealmeansforasurfacevesseltoresumeana0ackingrole. (ExtractfromStevensD.M.TheImpactofSubmarineThreatonAustralia'sMariGmeDefence1915-1954,UNSWADFACanberra,2000.pp.51-52). From1940onwardsAdmiraltyandtheNavalBoarddiscussedthepossibleusesoffixedASDICinDarwinHarbour.ThesuggesGonwasforASDICtobefi0edtodolphins(pylonsorstandsfixedtotheseabed)butthiswasconsideredunsuitablebecauseofthenatureoftheseabedandGdes.ConsideraGonwasalsogiventofisngType135DetectorUnits,afixedASDICthatwassecuredtoaship'sside,totheboomworkingvesselsandthegateships.Eventuallyonlythegateshipswereequippedwiththisin1943. PortWarSignalStaJon DuringGmesofwar,theNavyhastradiGonallyestablishedWarSignalStaGonsoncoastlinestocommunicatewithshipscomingwithinvisualrange.ThoseattheentrancestoharbourswerecalledPortWarSignalStaGons(PWSS). Asradiosilencewaso]enimposedonshipsduringwarGme,thefirstcommunicaGonashipwouldhavewithNavalHeadquarterswaswhenitsbridge'Gpped'thehorizonandMorsecodechallengeswereflashedtoandfromthePWSS. Darwin'sPWSSwaslocatedhalfwaybetweenDudleyPointandEastPointwithit'sstaffarrivingon27August1939.Wirelesstelegraphywasinstalledby6October1939andtheindicatorloopstaGon(hut)wasestablishedatDudleyPointby10October1939.Ofthe60feethighsignaltower,nothingremains.ItwasinaposiGon1080feet,bearing009½°fromtheTriangulaGonStaGonatDudleyPoint.Thereferencepointdoesn'texisttoday,butastudyoftheareasuggestsanavigaGonalbeaconwaserectedontheendofDudleyPoint.Thiswasprobablyonasinglepole.Asurveyor'splaqueonthecliff'sedgemarksthespot.

� AerialViewofBoomNet. UnGl1943theindicatorloophutwasalsolocatedatthePWSS.DanAllison,asignalmanbetween1941-1943recalled,...'becauseoftheindicatorloopwehadclosecooperaGonwiththe[Army's]searchlightba0eryatDudleyPointandtheArmy'sba0eryatEastPoint,whichwerealwaysalertedifacrossingwasrecordedovertheloop'.Therewerebetween35and40navalpersonnelatthePWSSbecauseoftheindicatorloop.TheCommandingOfficerwasLieutenantA.B.Smith,RANVRwhowasalsotheExtendedDefencesOfficer.Anotherofficeractedassecondincommandandbelowhimwere,fourraGngwatch-keepers,anERAtomaintainthegenerator,fivewirelesstelegraphyoperators,oneYeoman(Pe0yOfficer)ofsignals,oneleadingsignalman,10signalmen,oneforadministraGon,onecookandassistant,onewardroomstewardandtwoworkmen.HMASMelville,(theDarwinshoreheadquarters)alsosentmenrecuperaGngfromillnessouttothePWSSforafewdaysataGme. DanAllisonalsorecallsthat'TherewerealsotwoABs,WWIveterans,whoweretakenonasguardsa]ertheJapanesecameintothewar.Theyweretheretoprotectusfromparatroopers,buttheycrackedunderthestrain

andonenightclubbedaW/TraGngontheheadwhenhewasoutoftheW/Tofficespendingapenny!'WiththewarGmeblackout,torcheswerenotpermi0edandmenwereforcedtogropetheirwayaroundinthedark. Photographicevidencesuggeststhestaffhadincreasedtosixofficersandatleastthirty-fivemenby1944. BlytheLindsay,signalmanatPWSSDarwinin1944recalled...'therewasanenclosedroomatthe[signaltower's]base,builtofconcrete,whichhousedasmallgeneratormountedatwaistheightonaconcreteblock.Thishadtobehand-startedtopowerthe10inchsignalprojectorthatwasusedtochallengeapproachingvessels.'CommunicaGonwiththeboomgateships,aboutamileandahalftothewest,wasbyvisualsignalsalsousingthe10inchsignallingprojectorfromthePortWarSignalStaGon,andsignalsfromthegateshipstothePWSSwaseitherbyAldislamp(ahand-heldsignallamp)orsemaphore. ThePWSSceasedfuncGoning12September1945. FollowingtheCessaJonofHosJliJes WiththecessaGonofhosGliGesinAugust1945Australia'sportswereclearedoftheiranG-submarinedefencesexceptforDarwinandFremantlewherethenetsandthebuoysweredismantledandstoredintheirrespecGveboomdepots.TheconcreteclumpsinDarwinHarbourremainedontheseabedincasetheywererequiredforfutureuse. InDarwintheindicatorloopwasli]edandwiththefixedASDICswereallreturnedtostores.KarangihadbeentransferredtoFremantle,anda]erdismantlingtheDarwinboomnetandbuoysKoalaandKangaroosailedforSydney.Kookaburra,KaraKaraandKoompartooremainedinDarwinandwereplacedinreserve. ConsideraJongiventoAnJ-TorpedoDefence LayinganG-torpedonetstoprotectthefleetanchoragewasdiscussedin1939butasthePacificwarmovedawayfromAustralianwatersthisideawasabandoned.However,anG-torpedonetswerelaidattheMantonDam,thetown'swatersupplyabout47milessoutheastofDarwin,underthesupervisionoftheBoomDefenceOfficer. ShippingMovementsofBoomWorkingVessels <tdstyle="border-bo0om:1pxsolid#D9DFE9;text-align:center;""="">31-8-45

Arrived Darwin Completed

Boom Service Kookaburra

20-11-39 15-1-46

Koala 29-4-40 12-10-51

Kangaroo 13-1-41 5-11-54

Karangi 24-1-42 9-11-46

Kara Kara 14-11-41 8-12-45

Gunbar - -1-41 - -2-43

Koompartoo 28-2-43

�

HMASKoompartoowesterngatevessel.Inforeground,sternofHMASKaraKarawithBWValongside.THESUN,2August1943.CourtesyoftheHerald&WeeklyTimesPtyLtd. TheAuthor Paton(Pat)ForsterjoinedtheRANRinOctober1940.FromOctober1941toSeptember1943heservedinDarwin,firstasasignalmanandlaterasadraughtsmanintheBoomDefenceOffice.A]erreceivinghiscommissionhejoinedHMASWhyallaastheanG-submarineofficerandcompletedhiswarserviceinthePacific.HewasdemobilisedaLieutenantRANVRinMarch1946. FooterInfo

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