What are ELF towers used for?

To my limited understand of the topic I understand the term "ELF Towers" to refer to the U.S. Navy communication station in northern Wisconsin situated on top of the Niagara Escarpment which is a HUGE rock formation that the Niagara falls flows over, hence the name. This formation juts all the way out to the Atlantic Ocean. The Navy used it as an antenna to transmit messages to submarines deep in the Atlantic since normal radio waves would not make it through the water Extremely Low Frequencies (ELF) are used. If I understand this correctly ELF waves are similar to infra-sound which detected far far away from the transmission site at very low power. This was used up until the late 90's when some other method became available. The ELF wave were known to cause harmful health and environmental effects. I have heard stories about environmental activists gathering at the tower site the same time every year to wage protest againced the use of the towers. A few people every year would cross in the restricted area and attempt to cut down the tower. It sounded to me like a highly organised event. Of coarse these people would be thrown in jail for a couple of years, today they would branded as terrorists and thrown in a dark hole some place.

I have heard the term also used in reference to cell towers but I dont understand why. hope this helps.