This means that the lower the frequency a radio transmission, the deeper into the ocean a useable signal will travel. Thus, the ELF system represents a critical safeguard against a scientific breakthrough in submarine detection by another nation using aircraft or satellite systems that exploit non-acoustic phenomena such as kelvin wakes and internal waves near the surface.ĮLF submarine communication systems make use of a principle in physics where the attenuation of radio signals (electromagnetic waves) from seawater increases with the frequency of the signal. The ELF submarine communication system permits submarines to receive communications without reducing speed or operating at the surface. This requirement imposes an enormous restriction upon the submarine's operating depth and its speed, as well as increasing its exposure to detection. With other submarine communication systems, continuous communication is possible only when submarines deploy a receiving antenna while operating at or near the surface. It is a critical part of America’s national security in that it allows the submarine fleet to remain at depth and speed and maintain its stealth while remaining in communication with the national command authority. The Navy’s ELF submarine communication system is the only operational communications system that can penetrate seawater to great depths and is virtually jam proof from both natural and man-made interference. submarine fleet to perform its mission, it must remain silent and be undetectable. The Clam Lake ELF radio station broadcasts messages to the fleet as required by the Navy Submarine Broadcast Control Authority in Norfolk, Virginia or Pearl Harbor, Hawaii. The submarine communication site has more than 28 miles of over-head signal transmission line that form part of the “electrical” antenna to radiate the ELF signal from the two-acre transmitting facility. The Clam Lake site, located in the Chequamegon National Forest in Northern Wisconsin, is the site where testing began for ELF communications more than 30 years ago. The sites at Clam Lake, Wisconsin and Republic, Michigan are operated by the Naval Computer and Telecommunications Area Master Station – Atlantic. Navy operates two extremely low frequency (ELF) radio transmitters to communicate with its deep diving submarines. To order a 100% USA made hat, please e-mail us at and we will process your order manually.The U.S. While all of our hats are embroidered by us in our Florida workshop, we have now obtained a reliable supply of US made hat blanks for those wanting a 100% USA made hat. Please e-mail us to let us know your circumstances if you need your order expedited!We now offer the option of 100% USA made direct embroidered ship and sub hats by special request for an at-cost surcharge per hat ($10.00). So please order earlier if possible to give your gift the best chance to arrive on time! If your order is for a birthday or ill veteran or other time sensitive occasion we are happy to expedite your order. While our normal order processing time frame is 3-4 weeks, during Christmas season all orders placed by December 18th SHIP before Christmas (but may not be RECEIVED if placed that late until after Christmas). To ensure timely delivery of any Christmas gift orders before Christmas Day, the sooner the better! Please note that all of our items are "made to order".
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