>>9508687yes I know about then
https://vizivtechnologies.com/I don't know if we are just misundertanding each others concepts but the VLF does penetrate ground and even water example of military use pic related is from a submarine training book:
https://maritime.org/doc/oberon/operations/index.htm#pg10ALK VLF aerial installed in recoverable buoy.
ALM Omni directional VLF aerial comprising a series of loops in the fin.
ALN Telescopic HF/UHF mast
ALW Buoyant, disposable VLF wire aerial
AMK UHF/IFF combined antenna associated with the ECM mast.
AWJ Emergency whip aerial for use on the surface only.
https://en.wikipedia.org/wiki/Very_low_frequency>Because of their large wavelengths, VLF radio waves can diffract around large obstacles and so are not blocked by mountain ranges or the horizon, and can propagate as ground waves following the curvature of the Earth.... The conductive ionosphere and the conductive Earth form a horizontal "duct" a few VLF wavelengths high, which acts as a waveguide confining the waves so they don't escape into space. The waves travel in a zigzag path around the Earth, reflected alternately by the Earth and the ionosphere, in TM (transverse magnetic) mode.>VLF waves have very low path attenuation, 2-3 dB per 1000 km,[2] with little of the "fading" experienced at higher frequencies... VLF transmissions are very stable and reliable, and are used for long distance communication. Propagation distances of 5000 to 20000 km have been realized.[2] However, atmospheric noise (sferics) is high in the band,[3] including such phenomena as "whistlers", caused by lightning. 