Why would the military interested in higher-frequency communications? I can think of a couple of reasons of the top of my head:
1) There has been significant pressure over the last couple of years from Congress (lobbied by commercial carriers) to reallocate spectrum from the federal government and to auction it to commercial carriers [3]. With increasingly advanced communications systems and waveforms being deployed in the military which require significantly more bandwidth, that means they have to do more with less. Shannon's law tells us that higher frequencies are capable of more bandwidth than the lower frequencies, which means high-frequency RF could transfer a lot more information than low-frequency RF systems [4]. This is important given the military's push towards buzzwords like "sensor fusion".
2) High-frequency communications systems are point-to-point rather than broadcasting over a wide area. Think of how light propagates from a laser pointer versus a light bulb. Low-frequency broadcasts, such as TV stations, propagate over a wide area of land from a single antenna. High-frequency microwave communications, such as the white cylindrical drums you see on cell towers, are directional and require the communication antennas to more or less be pointing directly at each other. There are three advantages of these point-to-point antennas: A) higher bandwidth, as discussed earlier, B) much lower likelihood of detection by your enemy, since your communications are targeted rather than broadcasted, and C) lower probability of interception by your enemy, because they would have to place an antenna directly in the path between your two links in order to capture your signal.
3) RADAR systems can be significantly more accurate in the higher frequencies, allowing more precise targeting and identification of targets. This has major applications both within and outside the military. The Doppler Radars are an example of a non-military application that provides weather information about the US [5]. The more accurate they can make the RADARS, the better they can distinguish between cloud formations and therefore provide more accurate weather predictions.
(Disclosure: I was previously involved in the battles between commercial carriers and US Federal Government regarding reallocation of spectrum. The statements in this comment are my own beliefs and should not be construed as the beliefs of my current or previous employers.)
[1] http://www.ntia.doc.gov/files/ntia/publications/2003-allochr... [2] http://www.mike-willis.com/Tutorial/PF5.htm [3] http://broadband.about.com/od/wireless/a/Ntia-Continues-To-I... [4] https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore... [5] http://radar.weather.gov/