VLF--a frequency so low, the waves will actually propagate through earth---and water. The Navy uses it to communicate with subs, for National Command and Control of nuclear subs and ICBMs. The wavelength is something measured in miles (2-4; can't remember).

The wire is as fat as your pinky because it is about 2 miles long!! (So it needs to be that thick to support the weight of 2 miles of cable). I believe it is weighted-down with about a 50lb weight on the end, so, as the E-6B (TACAMO) circles overhead, making the weight almost stationary, the antenna wire scribes a cone above it--remaining almost vertical.

I'm pretty sure each antenna is used one time, then snipped-off--too hard to reel back in.