Radio vs Infra Red communication
For defence applications where detection of radio signals by opposing forces is a potential problem there is an alternate solution; infra red (IR).
Using IR for short range mobile communications ensures that the signals will not be detectable only a few metres away from the zone covered by the system. This compares to possible detection of radio signals many miles away for even relatively low power radio systems. Longer range communication is also possible using infra red; ship to ship communication can take place in complete radio silence.
In terms of cost an IR communication system can be broadly comparable to a radio frequency system so why do current naval projects seem to favour communication solutions that in radio detection terms light up a warship like a Christmas tree? Good question but if you don’t want to advertise your presence to anyone with a radio receiver and/or simple direction finding equipment, think about using IR.