The Germans had great difficulty in communicating at any distance over a few miles on their upper HF and VHF radios, as good as they were. After some research the German Army started to use horizontally polarized high angle communication in the 2 to 6 mHz frequency range for much of their communication. Despite the low solar activity of sunspot Cycle 17, which peaked in 1937 and was decreasing for most of World War 2, (Cycle 17 ended in February 1944,) the German Army found that high angle lower HF communication was virtually 100% reliable, and improved their ability to communicate and to coordinate movement and counterattack among elements separated by dozens to hundreds of miles across the varied terrain of the Eastern Front. This communication advantage was one reason that Russia, despite huge manpower advantages, and having what was arguably the overall best tank of the war (the T-34) had such trouble advancing against a far smaller German opposition.
The US, which had its own issues with battlefield communications, and which ordered the virtually complete destruction of the German radio manufacturing capability after WW2, missed learning this lesson until Vietnam. There the US Army, faced with difficult terrain, in which line of sight might only be a few miles, and in which the presence of triple canopy jungle vegetation added to the attenuation of VHF signals, rediscovered the virtues of high angle horizontally polarized radio communication. By lowering their whip antennas to the horizontal, and using lower HF frequencies, the US Army was able to use what we now call Near Vertical Incidence Skywave (NVIS) communication to good effect.
There are several advantages to NVIS; it is much harder to DF, except at relatively close distances, unlike LOS VHF and UHF communications, it can provide reliable local area to regional communications out to perhaps 500 miles with minimal power and very simple antenna installations, and unlike amateur repeaters, it does not require any infrastructure to work for local and regional communication. Antennas are easy to put up and can be very compact and portable. I have worked stations using NVIS on 160, 80 and 40 meter amateur bands using antennas just a few feet off the ground, and with power levels of just a few watts to no more than 100 watts.
I've worked stations up and down the East Coast with 5 watts during the day on a simple 40 meter dipole antenna. What is even more interesting is that a lower antenna works better. Our Field Day station had 4 operating positions this year and we made almost as many contacts running NVIS at 20 feet on the lower HF bands during the day than the other three positions combined.
Sparks 31 (link here) talks about this on his website, and so do other people. See links here, here and here. Having the latest whiz-bang digital encrypted VHF radios may keep some people from understanding the content of your communication, but it will not prevent them from knowing that you are transmitting, or from DFing you. A better investment might be a small portable all-mode HF/VHF/UHF rig like the FT-817 or the larger FT-897, but more important than either is the skill and knowledge to know when and how to use the gear. Gear can be bought, if you have the scratch, but skills take time to inculcate.
What is the purpose of communication? Ideal commo systems allow you to transmit information to your friends, and not only to deny the content of your communication to your enemies, but further to deny them any knowledge that communication is happening in the first place. If one cannot keep the enemy from knowing that communication is happening, it is nice for them not to know who is talking! NVIS is one arrow in your communications quiver that is nice to have.
if you do not understand what I'm talking about, O gentle reader, it behooves you to learn. I've been active, off and on, in amateur radio since my mid-teen years, and the skills I have learned may help stand me in good stead in the future. Most areas here in these presently united States have an amateur radio club offering courses at very low or no cost. Many people, from 9 to 90, have passed their tests and gotten their amateur license, and so can you and the advantages of having the skills that the license allows you to learn are substantial.
With regard to all who serve the Light and hoping I will hear some of you on the air,