National Geographic : 1950 Jan
Hurricane Waves Find No Masonry to Batter; Rebecca Shoal Light Stands on Stilts This unattended light, 50 miles west of Key West, directs traffic between Gulf of Mexico and Straits of Florida. Its automatic flash warns of a treacherous reef lurking beneath a calm sea often as shiny as crinkled tinfoil or molten lead. A working party of the United States Coast Guard here pays a duty call. together under water at old swimming holes knows how sound travels through water. But it goes faster than through air. And in Sonar a different wave, a supersonic one of pitch so high the human ear can't hear it (like a dog whistle), is used. This wave, or "ping," is sent from a pro jector in any desired direction, and made to "feel around" like a searchlight hunting some thing in the dark. When it strikes an object in the water, a Sonar microphone picks up the returning echo. Other instruments magnify the echo to make it audible to men's ears; still another records the distance and direction from which the echo bounces back; and yet another flashes a "firefly" on a screen to show its location. Finally, all these facts are recorded on paper. A higher pitch of your ping echo indicates an approaching target; a lower pitch means it's going away. In sea water (say at 390 F.) sound goes at the rate of about 4,000 yards in 2' seconds; so, if you send out your ping and it bounces back in 2' seconds, you know your enemy is only 2,000 yards away. You know where he is by the direction in which your projector is pointing when you get back the ping. Now both Navy's submarines and surface ships are Sonar-equipped. When students have been thoroughly grounded in Sonar work at this Key West shore school, they take to the sea in patrol vessels and destroyers-antisubmarine vessels of the most effective types-and simulate attacks as in actual warfare against our own submarine fleet, training in these waters. Submarine Training in Key West Waters Today at least two-thirds of antisubmarine education is imparted at this Key West school, disproving that old-time naval officer who, when the Naval Academy at Annapolis was planned, complained that "you might as well try to teach a duck to swim in the attic."