’ ep Joint Ta force SEVEN Task Group 7.3 ‘wasnington 25, D. C. Qveration Plan 31 December 1953, 12C0R CTG 7.3 No. 1-53 AppendixAnnex HydrophoneContact DeveloprentProcedure ENI.EIOK Atoli 1. General. The underwater detection system in use is the Acoustic Syste hark 6 nod 0, a passive listening device which receives underwater sounds in the audio frequency band. Pairs of hydrophones are connected by submarine cable to the control equipment ashore. A line of hydrophones, spaced 300 to 350 vards apart, is located on tne bottom across the Deep “ntrance and across the ‘Nde tassage of ENIWETOK Atoll. The rectangular area surrounding each pair is the aporoximate area in which that pair of hydrophones might be expected to detect the presence of a submarine attempting to enter throuch the channel by stealth. These areas are numbered to correspond with the tactical numbers of the respective pairs of hydrophones, numbers one through three being located in the Deep Entrance and numbers four throuzh seventeen being located in the “fide Passage, This system is not capable of discrininating between an underwater contact and a surface contact, nor positively between a large ship and a smaller craft, This requires that cach contact via hydrophone te checked visually, if possible, or else by radar to ascertain whether the suspected contact is a surface contact, and if on the surfrc:, the typ: of ’ contact. Because of the experimental nature of the Mr & Mod C Acoustic Srstem, the contict reports indicated in Annex J (Contact and Identification Dvelon- ment Procedure) and tased solely on ki 6 Lod O Acoustic 3vstcm indication shall not be sent to addressees outside of the Forward area except by CTC 7.3, 2. Tasks: as TE 7.3.6.0 (Underwater Detection Eloment) shall: (L) Report suspected contacts by telephone, and/or radio on ti: narbor circuit 2716 kes, to CTU 7.3.8 and to CTE 7.3.1.0 using tne following message system: CODE MEANIUG MCG NOG =~ Underwatur Detection Unit. ] THROLGK 17 - Station number of hydronhone indicating contact. RAD - YELLOW Definitely unfriendly contact, WITS ea ~ - Unidentificd sontact. All clear. Contact definitely identified as false or as friendly. J-I-1 CEANGS #1 POC4ve