Planting a hydrophone anchor with the cable attached.On the GUIDE.Hydrophone would pick up sound from RAR TNT explosion.
3/20/2019 12:32:34 PM
Date: 1924
Credit: C&GS; Season's Report Luce 1924-49
Location: Oregon, Cape Blanco area
Subject: Charting
Subject: Navigation
Subject: Electronic
Subject: Radio-Acoustic Ranging